M4 Mac mini stuck at 4K/8K 30Hz

The Technical Specifications for the M4 and M4 Pro Mac minis say that provided that you limit yourself to at most two displays, one of them can have "up to 8K resolution at 60 Hz".

• "Up to two displays: One display with up to {5K (plain M4) / 6K (M4 Pro)} resolution at 60Hz over Thunderbolt and one display with up to 8K resolution at 60Hz or 4K resolution at 240Hz over Thunderbolt or HDMI"

If you are using HDMI to make the connection, are you using a certified Ultra High Speed HDMI cable?

https://www.hdmi.org/spec21sub/ultrahighspeedcable

Those are the only HDMI cables designed to ensure support for uncompressed 8K @ 60 Hz video.

Also, how long is the cable connecting your Mac mini to the 8K TV set? I have read that modern versions of macOS are fairly intolerant of transmission errors – as in, they don't want to see any, and will cut resolution or even drop the video signal entirely in response to reports of errors. The longer the cable, and/or the lower quality of the cable, the more likely that there will be transmission errors.

kenofstephen wrote:

I have a few other devices attached to the same Denon 8K receiver to my Samsung 8K TV and none of those have had experienced the same problem like this.

The Mac mini's do not do well using long inferior HDMI cables or being patched thru devices like Switches and Receivers.

For the best results, connect the HDMI Display (Samsung TV in your case) directly to the Mac mini using the shortest possible certified high speed 8K HDMI cable.

The Mac mini needs to poll and identify the Samsung TV each time they are re-connected.

I would by-pass the Denon 8K receiver and connect the Mac mini directly to the Samsung TV using a separate high speed certifies HDMI cable. Then I would switch the TVs HDMI input between the Mac mini and Denon 8K receiver as needed.

Please try restarting in Safe Mode, if that doesn’t do it give AppleCare a call.