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OnePlus update blocks downgrades and custom ROMs by blowing a fuse
(consumerrights.wiki)
This is a most excellent place for technology news and articles.
I believe thay all have shitty operating systems. But some of them have an aftermarket OS available. Pick your OS first, then look for a phone that can run it. Here are the ones I know of:
GrapheneOS
CalyxOS (on hiatus)
Crdriod
LineageOS