What do you mean how? Something in base changes, the author of a package didn't put strict enough compatibility on their package and now you can't use the package. It's especially great when this sort of thing happens after spending ten minutes waiting for precompilation an hour for your time to first gradient and three days for a run to complete and you trusted the tool to let you write the results to a CSV using the CSV package(one of the most widely used packages). Then you file a bug report and get gas lit, so you just patch your local Julia version and compile it yourself so you don't wait 4 months for an upstream fix. Good times.
Counter anecdote, I had to go back to a quite complex project that a was developed in 1.5, 3 years ago, hundreds of dependencies.
Upgrading to 1.9 RC2 required changing a single dep (Light raps to the drop-in Graphs) and a single line (a library changed the return from a String to a StringView)
At this point the only thing I can say is. Have you ever been a Julia user? Or are you actively developing Julia? If you are actively developing Julia, yea sure pull down the feature branch after someone's reported a bug, hot fix your toml to point too some specific version after reading ten diffs to be sure you have the right one, maybe stand up your own package server or pay 50k for one from julia computing, recompile Julia itself and everything is totally fine! If it's not no big deal just stomp over the type with your own code, yay. Maybe that's even part of your job. If you're a user expecting to do development and receive updates on packages or language, all I'll say is best of luck.