Originally Posted by Ira L
So are you saying the second Thunderbolt monitor maxed out the TB4 capabilities?

To be specific on the Mac mini...
Originally Posted by Apple
Simultaneously supports up to two displays:
One display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0

Thunderbolt 3 digital video output supports
Native DisplayPort output over USB‑C
Thunderbolt 2, DVI, and VGA output supported using adapters (sold separately)

HDMI 2.0 display video output
Support for one display with up to 4K resolution at 60Hz
DVI output using HDMI to DVI Adapter (sold separately)
So although the computer can drive two displays, one of those must be HDMI and the HDMI signal may be carried via one of the two Thunderbolt ports or by the HDMI port built into the Mac itself.

The identical M1 SoC on the MacBook...
Originally Posted by Apple
Simultaneously supports full native resolution on the built-in display at millions of colors and:
One external display with up to 6K resolution at 60Hz

Thunderbolt 3 digital video output
Native DisplayPort output over USB-C
VGA, HDMI, DVI, and Thunderbolt 2 output supported using adapters (sold separately)

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein