Obviously sync will not work until reconnected. Also some features are disabled, the AI search for example. The ability to rename albums. Most of the features that do not work offline are noted under the feature in Victoria's book: Edit Like a Pro book: https://www.lightroomqueen.com/shop/
I have yet to see any information from Adobe about what works offline, but to be fair to them, I stopped using their help system a year or two ago.