Is it hard to install and calibrate the 2021 Apple TV for a total non-techie?

It is really simple to do. Please read the directions in https://support.apple.com/en-us/HT205358. Does the Denon have HDMI pass-through?

My Denon has HDMI ports/slots - is that the same as "pass-through"?

Video passthrough refers to having both HDMI-in and HDMI-out. But you may not want to use that, if the receiver is relatively old, and the AV receiver has lesser support for video resolution and dynamic range than the TV.

Instead you may want to use the TV for audio passthrough, depending on the specifications.

Please be specific and share the model number of the Denon, so that we can look up the specifications. And also share the model number of the Samsung smart TV.

Denon AVR-2113CI

The unit was made (2012) before HDMI 2.0 and HDCP 2.2 (2013), so commercial 4K passthrough is unfortunately not supported.

Samsung UN55KS8000

A 2016 4K LED TV with Tizen 2.4 OS and 4× HDMI 2.0/HDCP 2.2.

Samsung is wall hung and very hard to access ports

I thought those Samsungs had the One Connect box, so you don’t have to access ports on the back?

I would suggest connecting as Apple TV →[HDMI]→ TV →[HDMI ARC]→ Receiver, so that you can take advantage of the 4K content available. Connecting with this model receiver as hub would limit the video to HD 1080p.