How do you connect an external display to the Apple Silicon iMac? What is the maximum supported resolution? Are adapters required?

All Apple Silicon iMac models -- the iMac "M1" 8 CPU/7 GPU/2 USB-C Shaped Ports 24" (2021), iMac "M1" 8 CPU/8 GPU/4 USB-C Shaped Ports 24" (2021), iMac "M3" 8 CPU/8 GPU/2 Ports 24" (2023), and iMac "M3" 8 CPU/10 GPU/4 Ports 24" (2023) -- can simultaneously support the internal 23.5" (4480x2520) display at full native resolution and a 6016x3384 (6K) external display at 60 Hz like the 6K Apple Pro Display XDR via a Thunderbolt / USB 4 (USB-C) port.

The Apple Silicon iMac models support both extended desktop (second workspace) and video mirroring (internal display duplicated on the external display) modes.

Smaller Thunderbolt 3 (USB-C) equipped displays also will work. It is possible to connect vintage VGA displays with the Apple USB-C VGA Multiport Adapter (MJ1L2AM/A), as well.

Can you wall mount the Apple Silicon iMac models? Are they VESA compliant?

As shipped by default, the Apple Silicon iMac models are not VESA compliant and not possible to wall mount.

However, at no extra cost at the time of initial purchase, Apple does offer these models with a "Built-in VESA Mount Adapter" instead of the normal stand.

Photo Credit: Apple, Inc. (Apple Silicon iMac - VESA Mount Option)

Unfortunately, there is no official way to convert one of the Apple Silicon iMac models that shipped with the stand into a VESA compliant model.

What type of video processor is provided by the Apple Silicon iMac? Does it have "integrated" or "dedicated" video memory? Is it upgradable?

The Apple Silicon iMac models all have a video processor (GPU) that is integrated with the SoC.

Typically, video processors with "integrated" memory, meaning that memory is shared with the system, tend to be lower performance than those with "dedicated" memory reserved for the video processor. However, benchmarks show that the Apple Silicon iMac graphics performance generally can hold its own compared to hardware at an equivalent price point.

It is not possible to upgrade the video processor in any Apple Silicon iMac model at the time of purchase or afterwards.

Does the Apple Silicon iMac support an eGPU?

An eGPU -- or external Graphics Processing Unit -- essentially is a graphics card in a box connected to a computer.

For any Intel-based Mac that has Thunderbolt 3 ports there are a variety of compatible eGPU models. However, these eGPUs explicitly are not compatible with Apple Silicon-powered Macs like the Apple Silicon iMac.

Perhaps in the future Apple will release its own compatible eGPU for Apple Silicon Macs, or allow third-parties to do so, but for now, the answer is simply no.

How can you "force" or "hack" the Apple Silicon iMac to run at native resolution or otherwise fit more content on screen than by defaul?

The "Display" control panel within the macOS provides some additional control to display scaled resolutions that allow more to fit on the Apple Silicon iMac display by default.

However, for many more options, you might like to try the QuickRes app. QuickRes is the self-described "quickest and easiest way to switch between screen resolutions on your Mac," Freshly updated for compatibility with M1-powered Macs like the Apple Silicon iMac, it supports Macs running OS X El Capitan (10.11) or higher and costs US$14.99.