I am happy to say I found a solution to this problem. I will share this here in case it could help anyone else. It turns out the latest March linux-firmware breaks the WiFi adapters for ThinkPad T14 Gen 3.
FYI A kernel update to 6.1-* fixes this but I have other painful problems there with black external monitors which is why I downgraded to 5.15.106 (the kernel I know and love from my home laptop Thinkpad x1 carbon)
[SOLUTION]
→ March 2023 Linux firmware breaks WiFi for ThinkPad T14 Gen3
List previously installed versions in local cache
ls /var/cache/pacman/pkg/linux-firmware-* -1
Manually downgrade to previous january firmware
sudo pacman -U /var/cache/pacman/pkg/linux-firmware-20230117.7e4f0ed-1-any.pkg.tar.zst
Reload driver
sudo modprobe -r iwlwifi && sudo modprobe iwlwifi
Tell pacman to ignore linux-firmware updates until this is sorted upstream
edit /etc/pacman.conf: ← use sudo for this
[options] <- section tag
IgnorePkg = linux-firmware