this is the stupidest possible reason for Gdocs to act up.
I use Firefox. there are a lot of sites that don't like that and throw a fit. So I normally have a User Agent Switcher enabled. This basically puts a hat and mustache on Firefox that says CHROME and it works just fine.
Mostly I find medical websites hate Firefox. But they are tricked by the hat that says CHROME. ah yes, definitely you are using chrome, totally fine! I will work for you now.
Gdocs decided to pitch a fit and not let me type in a document I owned. Went through, did all the usual things, restarted browser, dumped cookies, turned off some other extensions. Toggled the Agent Switcher through a couple versions of Chrome, nu-unh.
Toggled it to a different version of Firefox. I haven't turned off the extension. Ah that hat that says FireFOX is fine! even though it does not match the Firefox you're using. Firefox is firend shaped!
Gdocs was really just "how dare you look at a google product with what appears to be chrome!?!?!? HOW DARE!!!"
BONUS: I can use the agent Switcher to lie about what operating system I am using too. So currently Gdocs hates all combos of Windows/Chrome (or chromium versions like Edge) but WILL let me do WIndows/Firefox, LINUX/Firefox, Mac/Safari.
Just no Chrome. It hates that specific hat, like a dog that hates a specific hat. You tkae that hat off right now or we are no longer friends!!!