ADB vendor key not correct?!

Hello again, sorry to be a pain. I'm still trying to get LineageOS onto my Nokia 6.1.

So far I managed to get everything, but now I'm stuck again at another point.
I've flashed boot.img all right, restarted into recovery mode, wiped the phone, and tried to sideload the zip file according to the instructions on lineageos.org as good as I understood.
What I got now was:
C:\Users\Niki\Downloads\platform-tools-latest-windows\platform-tools>adb -d sideload lineage-22.2-20260812-nightly-PL2-signed.zip

adb: sideload connection failed: device unauthorized.

This adb server's $ADB_VENDOR_KEYS is not set

Try 'adb kill-server' if that seems wrong.

Otherwise check for a confirmation dialog on your device.

adb: trying pre-KitKat sideload method...

adb: pre-KitKat sideload connection failed: device unauthorized.

This adb server's $ADB_VENDOR_KEYS is not set

Try 'adb kill-server' if that seems wrong.

Otherwise check for a confirmation dialog on your device.

What does that mean? My unlocking procedure yesterday was successful as far as I understood and the phone stayed unlocked. Or is this referring to something different?
How can I safely proceed now?