I also tried another 16 GB SD-card with the same result. The cards are ok. I can read the vfat-partition containing system-boot on my workstation running Linuxmint. Also the writeable-partition (ext4).
Every other image (buster, ubuntu-server and so on) I write to the card is booting fast and without
problems.
Watching the green LED of the Raspberry now it does not blink. The raspi is up for five minutes now. The monitor is an ordinary 19" HDMI one.
Just now the green LED blinks again about less than one time a second, irregularly, and now it stops blinking again.
Don't know what's wrong. I downloaded the Image again and wrote it to card ten times or so because I thought maybe it's corrupted. Compared the checksums, all ok. The unzpped image is exactly 5,0 GB (5.000.000.000 Bytes). I am wondering about that precise bytes indication showing a smooth integer.
Andreas