iPhone not showing up in the sidebar

Try resetting SMC. Then restart normally and check.

Also, boot into Safe Mode. Does the phone show up then?

Try: About This Mac, System Report, and check for presence of iPhone on the port you have connected it to.

If none of these suggestions work, download and run Etrecheck, provide full access, then post the output using the "Additional text" button below. It may reveal something that is installed that is interfering.

Is the iPhone unlocked?

In the Finder, if you go to the menu Finder > Preferences > Sidebar

is CDs, DVDs and iOS Devices checked?

MtD

Just a wild thought, but is the phone set up with the same Apple ID as the Mac?

Are you logged into the Mac as the administrator?

MtD

Completed all recommended steps offered by Apple's Support page results doing a search using:

"If your device doesn’t appear in the sidebar when connected to Mac"

Everything is in order although still didn't show in finder.

I used command+K to connect to an external back up drive and once 'connecting as'...the server and all network devices showed up, including my XS Max.

Hope this helps someone.