Sidebar automatically appears when I move cursor to left edge of webpage in Safari - really annoying! How to disable?

There is a workaround. Instead of switching Safari into Full Screen, maximize it by dbl-clicking each edge which will snap the window to the edges of the screen. You lose a tiny bit of screen real estate but no more sidebar popping up.

Your only other option, especially if you use Safari in full screen mode (and mission control) is with the dock set to the left side (>System Preferences>Dock.)

Enter this command in Terminal, copy and paste :

defaults write com.apple.Dock autohide-delay -float 1000 && killall Dock

This will fix the issue.

Side Note: the dock will need the Mission Control "four finger swipe up" see >Sys Pref>Trackpad> More Gestures to show/hide it.

the default in terminal copy and paste:

defaults delete com.apple.Dock autohide-delay && killall Dock

Sorry, at present there is no option available to disable this FullScreen mode feature.

You're welcome again. 😎

You're welcome.

I've been using Macs for 30+ years and there is still much I don't know. For instance I didn't know about snapping to the edge of the screen until it a few days ago when another user complained about the "feature" and wanted to disable it. He was accidentally dbl-clicking on the edges.

Once I learned you could snap windows to the edges, I just tried it with Safari and saw the Sidebar didn't open.

Aren't you glad you asked? lol