Assuming you are scanning for DVB-T broadcasts you could try manually entering a known good mux for the relevant transmitter and do a network scan. It works for DVB-S but I’ve never tried it on DVB-T.

Yes, it's for dvb-t2.

I'm not sure, from pieceing information on the Internet, apparently the scan presets that come with Tvheadend come from here:

https://git.linuxtv.org/dtv-scan-tables.git/log/dvb-t/es-Collserola

, and they have not been updated since 2014. I found some references to variants of w_scan, and w_scan2 seemed well maintained, but it's not giving me great results.

How standardised are DVB-T2 implementations across Europe?
Is there a generic scan preset for all of Europe that you could try?

But you don’t need to use the predefined muxes. As you say way out of date and useless. If you are installing TVH via the Wizard, when you get to the section Add predefined muxes just press the Cancel key. Then go into Muxes section, add the information for the one known working mux manually and TVH will will scan the whole band and add what it finds broadcasting.

If you want to do a manual scan outside of TVH I suggest using dvbv5-scan. It’s a lot more efficient and explained in detail here. It should be available to install from your package repository https://manpages.ubuntu.com/manpages/jammy/man1/dvbv5-scan.1.html

3 months later

Well, my dad complained about some missing channels. I played with dvbv5-scan without much success. In the end, I tried the --Generic--: auto-With167kHzOffsets scan preset in TVHeadend and that seems to have produced "all" the channels. Just recording this here in case it helps someone.