You are right, React Admin does bring MUI in it's own dependencies.

However I believe package managers that use PnP (namely PNPM) are more strict regarding the dependencies: if you import from, say, @mui/material, directly in your own code, then you need to add an explicit dependency on @mui/material. The transitive dependency through react-admin is no longer sufficient.

Also, React Admin v5.6.4 included a fix to improve compatibility with some package managers, namely PNPM.

Does using this version help fix your issue?