i can't install high sierra
how can i install high Sierra on Mojave 10.14.6 b/c my mac is geting busy
MacBook Pro 13″, macOS 10.14
Question marked as
Revert your Mac to a previous macOS version - Apple Support
Bottom line is you must erase your drive before you can install a previous OS. If you have backup from before you upgraded, you can restore that. However, you will lose any files you altered while on the newer OS.
If you don't have a backup, it is you must export any Library-based content (Photos, iTunes, Mail POP accounts, etc) and then import that back once you install the older OS.