Dell inspiron 5567 laptop, Ubuntu 20.04.3 LTS Long term boot problem with weird patterns

From the comments...

Reset the Power Manager. Shutdown your computer. Hold down the POWER button for ~20-30 seconds. Reboot and retest.

Check that the AC power supply is properly charging the battery when plugged into AC.

Test your AC circuits with a cheap AC plug-in wall socket tester from your local hardware store, or Amazon. It'll show incorrectly wired sockets, or bad grounds.

https://www.amazon.com/Bastex-Tester-Receptacle-Indications-Electric/dp/B071FVB35Q

Update #1:

Followed the instructions. First couple of times the laptop booted unplugged without any problem. I hope it lasts.