IWW comes to mind. They’re not aligned with any particular trade etc, unlike most unions.
Also…. See “You Deserve a Tech Union” recently published. If cost is an issue there is an arrangement that can be made, see author’s masto acct.
Personally, I was hired fully remote, and would fight like hell right beside you any attempt to drag me back. I’m fortunate to be four plus hours from the office I’d likely work in otherwise, so I do t expect to need to fight - I lived here when they hired me.
Whatever you learn and whatever options you find, please come back and post as it will help others.