I've seen other reports of dock issues on 3.5.5. I myself have a problem with muted audio output that I can't resolve outside of using the desktop mode and manually selecting the audio output I need (I have to stay in desktop mode for it to keep working).
Sigh. I had previously taken my Deck on the road a few weeks back for the first time, and I ran into unrecoverable issues then that kept me from using it until I could get back to a computer and USB drive. Right after I reinstalled the OS, I ran into yet another bug in the UEFI firmware - do NOT choose to restore defaults on firmware 118 or you'll lose audio and touch. The only way to recover from that was to downgrade the firmware and then upgrade again.
I genuinely love the Steam Deck, but the number of hard-to-resolve bugs lately has been HIGH.
If you can still roll back to the previous OS version, that should fix it for now. Hold down the [***] button during boot up and select the previous version.