Apple supports macOS migrations back several releases, but you can wind up with too big a gap.
Many people remember Mac OS X 10.6.8 fondly. Not just 10.6 Snow Leopard, but particularly its very mature 10.6.8 release, the final one in that series. It’s considered a stable and perfectly fine version. It’s not a problem—until they want to move to a newer system, particularly macOS Catalina or Big Sur, and find there’s no migration path.
Apple offers Migration Assistant both when setting up a Mac (whether new or erased) and as an app within macOS, particularly to migrate user accounts and applications. As a source, you can use a Time Machine backup, a disk image copy of your macOS startup volume (via a cloning app, for instance), or another Mac.
But Migration Assistant has its limits: in Catalina and Big Sur, you must migrate from Mac OS X 10.11 El Capitan or later. Attempts to copy from older installations lead to an error.
Read more at MacWorld.com