Hello, sheryll66.
I'm sorry that you're having this trouble with the Mac.
I would only consider downgrading the OS if you cannot find a remedy otherwise. Downgrading is not trivial and will require that you wipe the internal drive and reinstall the OS from recovery mode. This is a last resort. You'll need to ensure first that you have a current Time Machine or other backup of your Mac and user data.
Instead, try this first.
If rebooting your Mac doesn’t fix things, see if the problem still happens in Safe mode (hold the shift key down at startup). It can take much longer to safe boot (10 min) so be patient.
How to use safe mode on your Mac - Apple Support
Safe mode disables loading third-party drivers, forces the OS to clear certain caches and logs and does other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's expected.
Does the problem persist while in Safe mode?
Exit safe mode by restarting your Mac normally and re-evaluate the issue again.
Also, ensure that you have no anti-virus, clean up or optimizing applications installed. These will very often interfere with the proper operation of macOS and cause more trouble than they claim to prevent. If you have these types of software, uninstall them per the developer's instructions, restart the Mac and see if the problem is resolved.
XProtect Explained: How Your Mac’s Built-in Anti-malware Software Works - How-To Geek:
https://www.howtogeek.com/217043/xprotect-explained-how-your-macs-built-in-anti-malware-works/