MacBook Pro 13'' (2020) with Dell TB16 I'm currently able to use an external monitor via HDMI connection thanks to Thunderbolt3Unblocker but very often after unplugging the dock my laptop restarts due to an error: this seems related to a problem in windows resizing, is there any solution to that?
Also, some other strange things are happening from time to time: twice or thrice in my 2 weeks of usage it happened that after unplugging and then reconnecting to the dock, the two USB-C ports of the side of the laptop where the dock was previously plugged in stopped sending any signal to the monitor, while the other two on the other side were still working fine (this seemed to happen after, when unplugged, I left the laptop go to sleep mode); display port connection is apparently not working at all, while mini display port works with a suboptimal resolution (but this is covered in this conversation: https://github.com/rgov/Thunderbolt3Unblocker/issues/28).
I'm using MacOs 10.15.7
From GitHubs description:

Many people file bugs here about their Dell TB16 dock.
The USB, Thunderbolt 3, and audio out ports should regain
functionality after installing Thunderbolt 3 Unblocker.
However, video output does not work. Unfortunately, this is out of
scope for this project.

It clearly states that video output (e.g. HDMI) is not supported by this project.
They further clarify:

For whatever reason, an update to macOS High Sierra broke support for the displays attached to the TB16.

and also mention to upgrade the firmware of the dock:

You could try performing a firmware upgrade on the TB16, which has been reported to restore video (HDMI output). However, the firmware upgrade must be performed from Windows.


There is also a Thread about this issue on Apples own forums, suggesting to try this GitHub project, yet it is older and untested on newer hardware/software (i.e. make backups of your system and know how to revert these changes!).
You could try to reset SMC, NVRAM/PRAM and boot into safe mode.
You could try a clean install, but it looks like this specific Dell dock is finicky with Apple hardware.