Wrecked my RPi 3B+ boot is looping now?

[HansOtten]

Check the power supply! And make sure the SD card you use is OK, low level check it.

Do not connect anything but a known good keyboard and HDMI display.

Burn a new fresh SD card with a fresh image (lite Buster) and connect a known good (not your current) power supply.
If that does not help, check the SD card holder not making contact.

Not much else you can do without being able to boot.

[lost]

It is a headless Pi so I connected a screen and keyboard. The last thing I see is polkit.servce just below the RPi logo and the flash a blue-screen and starting again.
Flashed a new SD-card with the Raspberry Pi Imager, used this card to boot but no change. Is the Pi really wrecked? Who can help?

What distro are you using raspbian/raspberry OS or anything else?

Tried to figure-out in my logs when was polkit started: This service is not present on my (also headless/minimal: No desktop environment installed at all) PI system running Domoticz. Nor it is present on a PC running Debian 10 with cinnamon.

=> Try flashing a minimal raspberry PI OS on your test SD: Just wondering if this may be a flaw in the system you use that came with a recent upgrade and may be also be reproduced using current install images as well.

Otherwise, you'll have to try to get clues from increased boot messages verbosity by modifying the file that configures the kernel command line on your SD image from a linux PC (or a windows one with anything able to mout/modify an Ext4 file-system).