As chased down by @ewenmcneill this is a Python 3.12 bug that is fixed in 3.12.5[1], in "gh-117482: Unexpected slot wrappers are no longer created for builtin static types in subinterpreters"[2] per the changelog[3]. Will Ubuntu backport a fix or update 24.04 to a newer 3.12.x? Who knows.
(The issue applies to multiple builtin types, not just 'list'.)
1: https://cloudisland.nz/@ewenmcneill/113830211688055241
2: https://github.com/python/cpython/issues/117482
3: https://docs.python.org/release/3.12.8/whatsnew/changelog.html#python-3-12-5-final