Uncertain if it has all the customization you want, but check out ArcMenu for GNOME
https://github.com/tau-OS/tau-arcmenu?tab=readme-ov-file
https://gitlab.com/arcmenu/ArcMenu

I stand corrected, .NET Core is open source and uses the MIT License.

As in
“We’ve finished taking all we need from the Mono project and implemented it into our proprietary .NET implementation for Linux, Android and iOS. Instead of getting flack for killing off Mono (which is open source and would’ve been forked anyways) we graciously give this old husk to the Wine project. We recommend that active Mono users and maintainers of Mono-based app frameworks migrate to .NET. kthnxbye!”

Good thing that it went to Wine I guess, as they do lots of work to get old Windows programs up and running in Linux and that often involves Mono.

Info that could help others help you:
House or flat?
Renting or owning?
How large an area do you need to heat?
How many rooms?

Temperature and savings:
Where I live they say that a house with people living in it should be at least 16°C (~60°F) to handle the moisture we generate.
Humans should have at least 18°C (64°F), preferably 20°C (68°F).
That means that you could close doors and let unoccupied rooms have lower temperature than the rooms you use.
If you’re stuck with space heaters then you’ll save quite a lot that way.