Well, it depends. If you have an API with only a few direct usages, you might do it in a single commit. Changing API's that have many usages is difficult to do atomically even if you have a monorepo, due to the difficulty of getting approvals and the risk you'll have to roll it back.

Often it's better to introduce a new function and migrate usages to it across multiple commits.

Either way, it's on you to fix everyone else's code, which is a different mindset from releasing a library and letting downstream users do the migration themselves when they feel like it.