Thanks @MichaIng! I would be happy to do it, the only problem on my side is that now I will not have physical access to the board (and as a consequence to the HDMI connection) for a while, possibly even for some months.
Is there another way to test it remotely? I guess not. 
Since we don’t know a clear kernel error that indicates whether HDMI works or not, no way to test remotely. And it would be risky anyway without physical access, in case some kernel build breaks boot or network.
It is not that urgent IMO: The DKMS issue is likely a rare one, specific to your particular driver sources, and now that we found the unintentionally missing RTW88 backport patch, that WiFi chip is generally supported already. And there is always the possibility to downgrade to package version 26.02.0-trunk-dietpi4.