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.
…
Continue here:
https://www.macworld.com/article/3597998/how-to-upgrade-from-an-older-mac-operating-system-to-macos-catalina-or-big-sur.html