diff --git a/core/object/class_db.cpp b/core/object/class_db.cpp
index dc28fa10de20..f5171f60ec6f 100644
--- a/core/object/class_db.cpp
+++ b/core/object/class_db.cpp
@@ -243,8 +243,11 @@ HashMap<StringName, StringName> ClassDB::resource_base_extensions;
 HashMap<StringName, StringName> ClassDB::compat_classes;
 
 bool ClassDB::_is_parent_class(const StringName &p_class, const StringName &p_inherits) {
-	StringName inherits = p_class;
+	if (!classes.has(p_class)) {
+		return false;
+	}
 
+	StringName inherits = p_class;
 	while (inherits.operator String().length()) {
 		if (inherits == p_inherits) {
 			return true;
diff --git a/scene/register_scene_types.cpp b/scene/register_scene_types.cpp
index a711d28c76ab..73507d36fc14 100644
--- a/scene/register_scene_types.cpp
+++ b/scene/register_scene_types.cpp
@@ -234,6 +234,10 @@ static Ref<ResourceFormatLoaderText> resource_loader_text;
 
 static Ref<ResourceFormatLoaderFont> resource_loader_font;
 
+#ifndef DISABLE_DEPRECATED
+static Ref<ResourceFormatLoaderCompatFont> resource_loader_compat_font;
+#endif /* DISABLE_DEPRECATED */
+
 static Ref<ResourceFormatLoaderStreamTexture2D> resource_loader_stream_texture;
 static Ref<ResourceFormatLoaderStreamTextureLayered> resource_loader_texture_layered;
 static Ref<ResourceFormatLoaderStreamTexture3D> resource_loader_texture_3d;
@@ -251,6 +255,11 @@ void register_scene_types() {
 	resource_loader_font.instance();
 	ResourceLoader::add_resource_format_loader(resource_loader_font);
 
+#ifndef DISABLE_DEPRECATED
+	resource_loader_compat_font.instance();
+	ResourceLoader::add_resource_format_loader(resource_loader_compat_font);
+#endif /* DISABLE_DEPRECATED */
+
 	resource_loader_stream_texture.instance();
 	ResourceLoader::add_resource_format_loader(resource_loader_stream_texture);
 
@@ -799,6 +808,9 @@ void register_scene_types() {
 #ifndef DISABLE_DEPRECATED
 	// Dropped in 4.0, near approximation.
 	ClassDB::add_compatibility_class("AnimationTreePlayer", "AnimationTree");
+	ClassDB::add_compatibility_class("BitmapFont", "Font");
+	ClassDB::add_compatibility_class("DynamicFont", "Font");
+	ClassDB::add_compatibility_class("DynamicFontData", "FontData");
 	ClassDB::add_compatibility_class("ToolButton", "Button");
 
 	// Renamed in 4.0.
@@ -918,7 +930,7 @@ void register_scene_types() {
 	ClassDB::add_compatibility_class("StreamTexture", "StreamTexture2D");
 	ClassDB::add_compatibility_class("Light2D", "PointLight2D");
 
-#endif
+#endif /* DISABLE_DEPRECATED */
 
 	OS::get_singleton()->yield(); //may take time to init
 
@@ -970,6 +982,11 @@ void unregister_scene_types() {
 	ResourceLoader::remove_resource_format_loader(resource_loader_font);
 	resource_loader_font.unref();
 
+#ifndef DISABLE_DEPRECATED
+	ResourceLoader::remove_resource_format_loader(resource_loader_compat_font);
+	resource_loader_compat_font.unref();
+#endif /* DISABLE_DEPRECATED */
+
 	ResourceLoader::remove_resource_format_loader(resource_loader_texture_layered);
 	resource_loader_texture_layered.unref();
 
diff --git a/scene/resources/font.cpp b/scene/resources/font.cpp
index f88082c665d6..7c17610df739 100644
--- a/scene/resources/font.cpp
+++ b/scene/resources/font.cpp
@@ -472,6 +472,32 @@ void Font::_data_changed() {
 
 bool Font::_set(const StringName &p_name, const Variant &p_value) {
 	String str = p_name;
+#ifndef DISABLE_DEPRECATED
+	if (str == "font_data") { // Compatibility, DynamicFont main data
+		Ref<FontData> fd = p_value;
+		if (fd.is_valid()) {
+			add_data(fd);
+			return true;
+		}
+		return false;
+	} else if (str.begins_with("fallback/")) { // Compatibility, DynamicFont fallback data
+		Ref<FontData> fd = p_value;
+		if (fd.is_valid()) {
+			add_data(fd);
+			return true;
+		}
+		return false;
+	} else if (str == "fallback") { // Compatibility, BitmapFont fallback
+		Ref<Font> f = p_value;
+		if (f.is_valid()) {
+			for (int i = 0; i < f->get_data_count(); i++) {
+				add_data(f->get_data(i));
+			}
+			return true;
+		}
+		return false;
+	}
+#endif /* DISABLE_DEPRECATED */
 	if (str.begins_with("data/")) {
 		int idx = str.get_slicec('/', 1).to_int();
 		Ref<FontData> fd = p_value;
@@ -899,6 +925,23 @@ RES ResourceFormatLoaderFont::load(const String &p_path, const String &p_origina
 	return dfont;
 }
 
+void ResourceFormatLoaderFont::get_recognized_extensions_for_type(const String &p_type, List<String> *p_extensions) const {
+#ifndef DISABLE_DEPRECATED
+	if (p_type == "DynacmicFontData") {
+		p_extensions->push_back("ttf");
+		p_extensions->push_back("otf");
+		p_extensions->push_back("woff");
+		return;
+	}
+	if (p_type == "BitmapFont") { // BitmapFont (*.font, *fnt) is handled by ResourceFormatLoaderCompatFont
+		return;
+	}
+#endif /* DISABLE_DEPRECATED */
+	if (p_type == "" || handles_type(p_type)) {
+		get_recognized_extensions(p_extensions);
+	}
+}
+
 void ResourceFormatLoaderFont::get_recognized_extensions(List<String> *p_extensions) const {
 	p_extensions->push_back("ttf");
 	p_extensions->push_back("otf");
@@ -918,3 +961,45 @@ String ResourceFormatLoaderFont::get_resource_type(const String &p_path) const {
 	}
 	return "";
 }
+
+#ifndef DISABLE_DEPRECATED
+
+RES ResourceFormatLoaderCompatFont::load(const String &p_path, const String &p_original_path, Error *r_error, bool p_use_sub_threads, float *r_progress, bool p_no_cache) {
+	if (r_error) {
+		*r_error = ERR_FILE_CANT_OPEN;
+	}
+
+	Ref<FontData> dfont;
+	dfont.instance();
+	dfont->load_resource(p_path);
+
+	Ref<Font> font;
+	font.instance();
+	font->add_data(dfont);
+
+	if (r_error) {
+		*r_error = OK;
+	}
+
+	return font;
+}
+
+void ResourceFormatLoaderCompatFont::get_recognized_extensions_for_type(const String &p_type, List<String> *p_extensions) const {
+	if (p_type == "BitmapFont") {
+		p_extensions->push_back("font");
+		p_extensions->push_back("fnt");
+	}
+}
+
+void ResourceFormatLoaderCompatFont::get_recognized_extensions(List<String> *p_extensions) const {
+}
+
+bool ResourceFormatLoaderCompatFont::handles_type(const String &p_type) const {
+	return (p_type == "Font");
+}
+
+String ResourceFormatLoaderCompatFont::get_resource_type(const String &p_path) const {
+	return "";
+}
+
+#endif /* DISABLE_DEPRECATED */
diff --git a/scene/resources/font.h b/scene/resources/font.h
index 226979c4a074..bc82a6fabfbf 100644
--- a/scene/resources/font.h
+++ b/scene/resources/font.h
@@ -198,9 +198,23 @@ VARIANT_ENUM_CAST(Font::SpacingType);
 class ResourceFormatLoaderFont : public ResourceFormatLoader {
 public:
 	virtual RES load(const String &p_path, const String &p_original_path = "", Error *r_error = nullptr, bool p_use_sub_threads = false, float *r_progress = nullptr, bool p_no_cache = false);
+	virtual void get_recognized_extensions_for_type(const String &p_type, List<String> *p_extensions) const;
 	virtual void get_recognized_extensions(List<String> *p_extensions) const;
 	virtual bool handles_type(const String &p_type) const;
 	virtual String get_resource_type(const String &p_path) const;
 };
 
-#endif
+#ifndef DISABLE_DEPRECATED
+
+class ResourceFormatLoaderCompatFont : public ResourceFormatLoader {
+public:
+	virtual RES load(const String &p_path, const String &p_original_path = "", Error *r_error = nullptr, bool p_use_sub_threads = false, float *r_progress = nullptr, bool p_no_cache = false);
+	virtual void get_recognized_extensions_for_type(const String &p_type, List<String> *p_extensions) const;
+	virtual void get_recognized_extensions(List<String> *p_extensions) const;
+	virtual bool handles_type(const String &p_type) const;
+	virtual String get_resource_type(const String &p_path) const;
+};
+
+#endif /* DISABLE_DEPRECATED */
+
+#endif /* FONT_H */