dotnet_title_bar VS tiny-js

Well for 32-bit foobar there is .NET Component Host + Title Bar component (foo_dotnet_component_host + dotnet_title_bar, previously called foo_title). If you want to make a custom skin you'd have to write it in XML, but there are several user skins for examples.

Not that one exactly, but you could make an exact replica using Title Bar (previously foo_title) and set that to appear at the beginning and ending of tracks. I guess you could even place it in exactly the same screen location. (Though I'm not sure if it might also pop-up on pause/skip and interfere)

So your best bet is the great time sink Titlebar (foo_title) and depending how much effort you want to put in (like everything foobar), you can either use one of these pre-made skins, or edit them in a text editor to see examples of the XML structure and design your own. The great thing is with a bit of graphics / image editing software to help out, you can make it look like anything.

You can always leave the main foobar window minimized and use Titlebar component mini- skins - see screenshots. They are basically just small "now playing" pop-ups.

For example, foo_title component is written in C# and it has a C# wrapper for C++ SDK: https://github.com/TheQwertiest/foo_title/tree/master/foo_title/fooManagedWrapper

Well it could be a foo_title skin (a "now playing" pop-up), but even if not, could certainly make one that looks just like it with foo_title.

(I say "rendered within" because some components render external windows outside the main foobar window, such as foo_title or foo_flowin - they also use their own transparency settings)

Titlebar (foo_title) - there are user made skins, or make your own to look like anything with XML.

tiny-js

Another possibility would be to compile a DLL from C/C++ code like https://levelup.gitconnected.com/integrating-native-c-c-libraries-with-unity-as-plugins-a-step-by-step-guide-17ad70c2e3b4?gi=1eb2bd2587cc . C and C++ have lots of implementations for other languages. E.g. https://www.lua.org/source/5.3/lua.c.html, https://github.com/gfwilliams/tiny-js, https://github.com/python/cpython and such