mem_sleep_default=deep
also doesn’t work. But I think I found the culprit:
I have a second M2 HDD in the WWAN slot of my laptop. Looks like on the first suspend everything is working fine, but the second time it somehow doesn’t get powered up again correctly, which causes the system to freeze. After I knew what I had to look for, I found similar topics on the internet. Seems like it’s a known problem with Lenovo laptops. The only thing I don’t understand is why everything was working for 1,5 years and then just stopped.
I tried some solutions I found on the internet to disable the drive on suspend or completely disable it in Manjaro, since only Windows is installed there, which I still need for my studies and recording music. But
sudo su -c "echo 1 > /sys/block/nvme1n1/device/delete"
only gave me a “Permission denied” 
For reference:
https://www.reddit.com/r/thinkpad/comments/k1gqb2/2nd_ssd_installed_in_wwan_port_on_t14_amd/