Got one step further after hard resetting: QR scan method etc. works, I triple checked that. I now get a proper "Couldn't connect" message with the red blinking, too. With the "fresh" device, I can now see all my local WLAN APs, too, so the WLAN interface does seem to work, too:
wpa_cli v2.9
Copyright (c) 2004-2019, Jouni Malinen <j@w1.fi> and contributors
This software may be distributed under the terms of the BSD license.
See README for more details.
Selected interface 'p2p-dev-wlp1s0'
Interactive mode
<3>CTRL-EVENT-SCAN-RESULTS
scan_results
> bssid / frequency / signal level / flags / ssid
82:a7:41:ec:80:f1 5220 -41 [WPA2-PSK-CCMP][ESS] lannisport_iot
76:a7:41:ec:80:f1 5220 -77 [WPA2-PSK-CCMP][ESS] lannisport
7e:a7:41:ec:80:f1 5220 -77 [WPA2-PSK-CCMP][ESS] lannisport_restricted
7e:a7:41:ec:80:f0 2462 -83 [WPA2-PSK-CCMP][ESS] lannisport_iot
7a:a7:41:ec:80:f0 2462 -44 [WPA2-PSK-CCMP][ESS] lannisport_restricted
7a:a7:41:ec:80:f1 5220 -77 [ESS] eighteenguests
76:a7:41:ec:80:f0 2462 -43 [ESS] eighteenguests
86:a7:41:ec:80:f0 2462 -83 [WPA2-PSK-CCMP][ESS]
70:a7:41:ec:80:f0 2462 -44 [WPA2-PSK-CCMP][ESS] lannisport
82:a7:41:ec:80:f0 2462 -83 [WPA2-PSK-CCMP][ESS]
ea:63:da:a4:f3:fb 2462 -79 [WPA2-PSK-CCMP][ESS] lannisport_restricted
ee:63:da:a4:f3:fb 2462 -80 [WPA2-PSK-CCMP][ESS] lannisport_iot
e0:63:da:a4:f3:fb 2462 -82 [WPA2-PSK-CCMP][ESS] lannisport
e6:63:da:a4:f3:fb 2462 -79 [ESS] eighteenguests
I have three APs, all providing the same four SSIDs (lannisport_iot, lannisport:restricted, lannisport, and eighteenguests). Could this be the issue, that the rae doesn't support any roaming or fails to connect to an SSID, when multiple APs are available to connect to it? It seems to "see" the nearest AP with both 2.4 & 5 GHz bands plus one other with 2.4 GHz only. According to the documentation, wpa_supplicant should support roaming, though.