Notepad in Win11 is getting Copilot, because of course it is, 1st to explain whatever text, and allegedly to create text in the future, but before you can ask Copilot to write something for you, you'll get spell check & auto correction -- it's already here in my Insider Beta copy. Now spell check & auto correction can be nice features to have available, but not for everything you might have open in Notepad. And while you can turn each off individually in Notepad's settings, turning it on/off, depending on whatever content you have in Notepad, would get old fast. I have a .txt file with common commands to use with the Command Prompt, and in all fairness Notepad didn't try to change anything, but having everything underlined in red was both distracting and annoying -- it was worth the few minutes to have a [hopefully] permanent solution, with a shortcut to the old Notepad on the desktop that I can drag whatever files onto.
To set things up I copied 2 files from the Windows folder in a copy of Win10 to a storage folder elsewhere -- the name and location of that folder is not important. I had to copy the Notepad.exe file, add a folder named "en-US", and copy/paste the "notepad.exe.mui" inside of it -- Notepad is hard-wired to look for that file *only* in that folder. I assume that those using another language will have a similarly named folder in Windows\. Then just create a shortcut to that copy of Notepad -- right-click -> copy Notepad.exe, then right click the Desktop -> Paste shortcut, naming it whatever you'd like.
The Neowin article that gave me the idea noted that you can uninstall Win11's Notepad, which sort of gives you the old version -- it's the same file but tabs etc. are now gone -- but that also loses file associations and such in the registry that you either have to add back or do without. My way everything about the *new* Notepad remains -- you just get an alternative when/if you want it.