@Virgo thank you!

Of course, the captive portal of the ap also stopped working. 

And it refuses access from the app.

I'll try to get the omadac version specified for the fw release running on something wired, maybe I can configure it this way?

  @NaN-Noyb so, to end this story:

I was able to join it to omadac,

Looks like omadac provides a fraction of the original firmware functionality. But I need VLANs, NTP, rsyslogd, portal, snmp, ...

I was able to factory reset the ap using the reset button and restored the config from backup.

No more tp-link firmware updates for tp-link ap's for me. Looking into 3rd party firmware or other vendors, sorry.