Okay, I made it. So here is my solution under arch linux.
- activating OEM unlock via dev. options
- if its not available it helped me to disable "auto updates" in dev options and return the date to anything in the past, then restart the device. If the OEM Unlock button is still not available, try other solutions
- Downloading and installing odin4 via paru
- go to linage repo and download vbmeta.img manually (https://download.lineageos.org/devices/a52sxq/builds)
- Open a Command Prompt in the folder where the file was downloaded and TAR the file by running tar --format=ustar -cvf vbmeta.tar vbmeta.img
- go to download mode via Vol. Down + Vol Up
- it will now ask you for unlocking the bootloader by following on screen information
- in the turqois screen it should say now bootloader state = checking+
- if not do a system update (this helped in my case. other say you must run the device with sim and wifi for 7 days or anything else. You must find your way)
- open up a shell in the folder where your tar file is located
- run odin4 -a vbmeta.tar
- when it reboots, remove the cable from the device (it just needs about 3 sec to finish the flash of vbmeta)
- delete userdata like described on the screen
- completly set up device, skip what can be skipped and shut down the device
- go to download mode via Vol. Down + Vol Up
- bootloader state said "broken" now
- download and extract the recovery zip and rename the recovery...img to simply recovery.img
- Open a Command Prompt in the folder where the file was downloaded and TAR the file by running tar --format=ustar -cvf recovery.tar recovery.img
- now flashing the recovery via odin4 -a recovery.tar
- it will immediatly restart the device once finished. Do not remove the cable. Make sure to immediatly hit Vol. Up + Power to boot into recovery mode. If you miss it, the device will reboot completly and you need to repeat this step.
- once in /e/OS recovery, perform a factory reset and then it apply update
- continue with the step "Install /e/OS" like documentated