If you are getting the crash:
Unexpected error: Vec3 cannot be cast to BlockPos
It is because whatever launcher you use persists the options.txt file between instances. The official Minecraft launcher does this. Its highly recommended to use a launcher designed for modded Minecraft, like:
Curseforge app
Modrinth app
Prism launcher
Multi mc
Poly mc
Alternatively if you want to keep using the official launcher, you can fix this crash by finding the options.txt file in your Minecraft folder. Set the value prioritizeChunkUpdates in that file to 0. Save the file and try to launch the game.