Cory Doctorow, on coining the term:
Here is how platforms die: first, they are good to their users; then they abuse their users to make things better for their business customers; finally, they abuse those business customers to claw back all the value for themselves. Then, they die. I call this enshittification, and it is a seemingly inevitable consequence arising from the combination of the ease of changing how a platform allocates value, combined with the nature of a "two-sided market", where a platform sits between buyers and sellers, hold each hostage to the other, raking off an ever-larger share of the value that passes between them.
The term was about online platforms degrading. This term described things like going to a subscription model, creating tiered subscription models, injecting more ads, and other practices to min-max short term profit on an online platform once enough customers were locked into it.
Since then a few examples I have seen referred to as "enshittification":
A movie sequel not being as good as the first movie.
A game sequel not being as good as the first game.
An unintentional quality defect on a one-time purchase of a consumable product.
A UI change to software (that didn't lock out previous features or change functionality) that the person personally didn't like.
The price of a new (luxury) product being higher than the complaining person would like.
A restaurant changing their menu.
A specific product being discontinued.
A TV show's writing getting worse.
The term has been so diluted it just means "a thing I don't like happened with any product or service."
I think the concept can legitimately extend beyond just online platforms. Not saying it isn't misused, but I think some of your examples can sometimes be the same basic problem:
Like a movie IP being acquired by a studio which forces the writers and directors to make changes in the sequel, to reach a bigger market or push merchandising or something.
Or a game production company forcing game developers to add micro-transactions.
Or new management from private equity forcing a reputable manufacturing company to use lower quality materials and defund QC.
I would broadly describe any situation where an intermediary business between creator and consumer makes things worse for both is enshittification. Online platforms are far from the only culprit.