And in this space, it's often a lot easier to get something autotools-based to build than something cmake or meson, at least in my experience. With autotools more often than not all I need to do is to specify the right target hosttriple and be done. With cmake and meson, it's often a fight to figure out how to cross-compile something like that.
This approach of cross-compiling for windows with mingw-w64, sometimes on "proper" linux, sometimes on WSL2, sometimes even on cygwin, seems to be still somewhat common in C/C++ land and in open source in particular, especially for projects that pull in a fair amount of dependencies (such as the aforementioned ffmpeg) - you will find a lot of Windows build guides that say only mingw cross-compilation from linux is supported and tested.
There are some projects that try to be partial dependency "package" managers for mingw, but for whatever reason I never really used them, so I cannot comment on how well they work and how up-to-date they are kept.
I guess, I just like fighting with the interwoven mess of build-systems and dependencies sometimes (and really, I don't spend more than maybe 1 or 2 hours a month on that)... a bit like people doing linux-from-scratch, except probably less time consuming than building an entire kernel and userland step-by-step.