Comment by colonwqbang

There is no built-in support that I know of. The official repos usually only contain the latest version of each package (Postgres being an exception).

However, every time I've needed older library versions I've found that somebody already uploaded a suitable PKGBUILD to AUR (Arch's user-contributed build-from-source system).

For instance, the current version of PHP in Arch is 8.2.6. If you need an older version there is php81, php80, php74, etc. available in AUR. If it didn't exist, just take the PKGBUILD for the current version, modify it to build the older version, then upload it to AUR so other people don't have to re-do the work. It works well in practice.