M$ Windows. All versions.
Windows was written to be highly complex to stop others trying to replace it or copy it.
WPF, .net, .net core, Winforms etc etc all add to the bloatware.
I do a lot of Windows dev work.
Someone somehow cocked up uploading selected files to a website in Visual Studio.
Instead you had to upload the whole website, a real pain and took ages.
I complained and they eventually fixed it.
Only to find on next revision it was back to square one !
FFS !
They fixed it again and then messed it up again
Currently it is back to fixed but who knows for how long.
A few years ago they removed C++ winforms and my program relied on it.
I complained and eventually it was put back in but only as an option.
I am now moved over to .net core which seems better and faster than C#.
Hopefully they wont mess that up or make it obsolete.