It took a long long time until Android emulators on Linux worked even close to what has been available on Windows.

The documentation says:

Waydroid uses Linux namespaces (user, pid, uts, net, mount, ipc) to run a full Android system in a container and provide Android applications on any GNU/Linux-based platform.

To my understanding this isn't even emulation but regular container technology.

Android emulation works better on it because the difference between Linux and Android is not that big

To be clear, the difference between Linux and Android is about the same as the difference between Linux and Fedora, in that they are both Linuxes. That's why this works, and why the reverse (running GNU/Linux apps and even entire systems on Android) is possible as well.

Although the Android kernel is slightly customized isn't it? I thought it exposed a few extra syscalls. How do these work on Waydroid?

I don't remember tbh. I installed it a couple of years ago but used it for the first only recently.

Yeah I tried it on pop os a while back and never could get it running at all

At what point did it not work for you? I just got it running on Fedora 40 following their wiki.

You need a custom kernel, or a kernel module plus DKMS and kernel headers for your current kernel.
You also need the package that handles whatever filesystem they use for their containers.
Then, you need to be running it on Wayland or else it doesn't work.
The part that I'm stuck on is running games, which gives an error about not being able to find libmain.so, which might be an architecture mismatch problem. Maybe I can virtualize that part? But at that point I might as well just buy a phone.

can you report your issues to the waydroid github or check on the fedora forums? the matrix and telegram chats are always open to help too if you have a bit of patience.