How to control Mac from iOS
Solution 1:
If you enable screen sharing on the Mac, you can use a VNC client to connect to it.
Several VNC clients exist for iOS. You may want to experiment.
Solution 2:
I've been using Chrome Remote Desktop for a couple of years. It's totally free, works across all platforms (macOS, iOS, browser, etc.), and uses your Google account for security. I like it a lot.