On a Mac mini, You MUST use the ThunderBolt ports on the back -- the front ports are USB-only and not fast enough.
¿Are you using EXACTLY pre-engineered ONE meter Thunderbolt cable that "shipped in the box" with this display?
if not, Brand-X ThunderBolt cables are limited to 0.5 meter, maximum.
if you need more length, you must use a [much more expensive, starts at US$125] ACTIVE ThunderBolt cable.
NB>> For this use, ThunderBolt 5 cables are not measurably superior, and do not allow you to bypass the length requirement. [ThunderBot-5 uses a modulated signal (multiple-bits per signaling interval) only when EVERY device is Thunderbolt-5 capable.]
Nest, be sure HDR is ON and the resolution is set to maximum the display can produce. If you like, you can use Text scaling to make text more readable:

nest, calibrate the display:
Calibrate your Mac display - Apple Support
[Edited by Moderator]