For this of us who wish to DO something, there's very little we can do except writing to our MPs, and Boycotting US companies where feasible.
So what feasible alternatives are there? Of course, most wil be a step down from the market leaders, that's why they're not market leaders.
MasterCard/Visa => Buggered if I know, or how to convince my bank even if I did.
YouTube => DailyMotion is probably as good as it gets

Prime & Netflix => iPlayer & NowTV, maybe piracy...

Amazon => Argos? Individual shops? - easily doable, "just" lacking convenience, especially for repeat purchases
Morrisons/Asda => Any other supermarket
Google => Qwant/Ecosia
ChatGPT => Mistral LeChat
Chrome/Firefox/Brave => Vivaldi
Microsoft => Linux

MSOffice=> LibreOffice
Starbucks/Costa => CaféNero/Coffe#1 or, of course, plenty of independants
McDonalds/PizzaHut/KFC => BurgerKing (Canadian), plenty of independants, and the likes of Pret, Greggs, Nandos etc
DuoLingo => Busuu
Any other big ones I'm missing? Any other viable alternatives? Obviously, it's going to be UK-centric, sorry.
Of course, also just trying to find alternatives to specific products