This is something I have thought a lot recently since I recently saw a project that absolute didn't care in the slightest about this and used many vendor specific features of MS SQL all over the place which had many advantages in terms of performance optimizations.

Basically everyone always advises you to write your backend so generically with technologies like ODBC, JDBC, Hibernate, ... and never use anything vendor specific like stored procedures, vendor specific datatypes or meta queries with the argument being that you can later switch your DBMS without much hassle.

I really wonder if this actually happens in the real world with production Software or if this is just some advice that makes sense on surface level but in reality never pans out. I personally haven't seen any large piece of Software switch to a different DBMS, even if there would be long term advantages of doing so, because the risk and work to retest everything would be far too great.

The only examples I know of (like SAP) were really part of a much larger rewrite or update rather than "just" switching DBMS.