SAMSUNG a10s boot loop after TWRP flash

I have bought a SAMSUNG A10s phone and tried to install TWRP according to this instruction. I was able to unlock the bootloader and enter the ‘Downloading’ mode.

I disabled time sycro and automatic updaten, set the time to a few weeks ago and connected the wifi in order to overcome the vaultkeeper.

I used a Debian computer and the Heimdall tool to flash this TWRP image into the recovery partition (which replaced the existing recovery.img, I took no backup – daft, I know).

Caused by the unlocked bootloader I got a warning with every startup. The usual key-combination for the bootloader menu did not work. So, after a few boot procedures, I tried the offered option to lock the bootloader and perform a factory reset.

Unfortunately, this brought me to bootloop. I was only able to enter the ‘Downloading’-mode again. Now, the bootloader is locked again but the images are invalid. I get this error message:

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Partition recovery
Reason recovery: Eroor verifying vbmeta image: invalid vbmetaheader
SAMSUNG recovery, A107FXXU7BTL1, 36415554R
SAMSUNG vbmeta, A107FXXU7BTL1, 36415554R

Quitting this ‘Downloading’ mode brings me back to the loop which reaches the SAMSUNG logo before it boots angain.

Can anyone explain this situation? Has anyone an idea for a solution? Using Heimdall, I can still read the PIT. So, maybe I can also flash any images. I am very glad for help!