"I have a Windows 11 workstation ... There's no lag with context menus or browsing directories with a lot of files."

You have the same Windows updates as everyone else and it will be painful. Also you should be keeping those CAD and games up to date and that will be very painful. Updates often happen at unfortunate times.

The Win 11 start menu has managed to be worse than the Win 10 effort and jumped to the middle of the task bar because ... reasons. Search on it is ever so slow. For some reason Win server 2025 has decided that I want to use a welsh keyboard (I'm english and tend to en_GB) when I RDP to one. Cymraeg (soz if I got "welsh" wrong) is alphabetically first in the en_GB list of keyboard mappings and I didn't even know there is a welsh keyboard! I suppose they must have some accents and diacritics not found in english. Its all just a bit weird that a bug like that surfaces after well over two decades of me using RDP from a Linux box to a Windows server.

You wag your finger at endpoint management in the same way that most software vendors used to do at AV back in the 90s and 00s (and 10s and 20s!) Its nothing new and basically bollocks! Modern AV is very good at being mostly asynchronous these days and besides, we have unimaginably faster machines these days and very fast CPU, gobs of RAM and SSDs. Copy a multi GB file and yes AV will take a while but at least you might be saved from nasties.

There is a good reason that corp devices have to run things like inventory agents, log shippers and the rest too - its about security. You doing your own IT security is fine and I'm sure you'll be fine.

You can get Win 11 to work on an old machine for now but as you say, you have to circumvent things. When you do that, I think you are storing up issues for later. Perhaps you will be lucky but perhaps not. My dad will soon be rocking Linux instead of blowing a grand+ on a new PC. He will get a secure booting Ubuntu based effort that looks quite similar to Win 11 that is fully supported by the vendor ... and me. I managed to "port" my wife some years ago and she is a much tougher proposition than my dad!