When to REINDEX a serial key?

Server: RDS Postgresql 12.5
Client: Vanilla Postgresql 12.5

Like most systems, we have lots of tables indexed on sequences.  Thus, all new keys are inserted into the "lower right hand corner" of the b-tree.

The legacy RDBMS which I used to manage has a tool for analyzing (not in the Postgresql meaning of the word) an index, and displaying a histogram of how many layers deep various parts of an index are.  Using that histogram, you can tell whether or not an index needs to be rebuilt.

How does one get the same effect in Postgresql?