> if you sell a device with a certain functionality and you later modify that device later to remove that functionality that is called theft.

It could be argued that it is not theft by various devious uses of legalise¹.

Personally I'd go with calling it, at best, deceptive sales practices (on the assumption that they knew they'd be moving this way long before they did), or possibly outright fraud if I'm in a less generous mood.

[FYI: Bambu A1 user for nearly two years, also have a Snapmaker U1, if I buy anything else it won't be Bambu unless their attitudes change. The A1/A1mini are still two of the best budget beginner printers IMO, though some clones come close, and I do recommend them if asked but with caveats around potential lock-in later and not believing promises due to a history of changed online posts, deliberately excluded from the WayBackMachine, and what to my understanding is an AGPL breach]

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[1] “There is a way to use the feature, so it isn't an attempt to permanently deprive”, or “you agreed to the possibility of such changes in the EULA”, and so on.