Blockintosh
Switch runtimes. Keep your worlds.
FEX and Rosetta now share worlds and add-ons within the same launcher profile. Profiles, accounts, Release and Preview keep their own content. Runtime settings stay separate, so you can change how the game runs without leaving your adventures behind.
A careful first move
The first launch brings older runtime folders into the shared library and keeps recovery backups. If two copies of a world differ, both are kept as separate saves. Conflicting pack versions stay in the backups; the launch log shows where to find them.
Back up before experimenting
Close Minecraft before creating or restoring a .bomprofile archive. Keep a separate copy of important saves before changing Minecraft builds, runtimes or mods.