Back in 2018 I had a problem with pihole using all interfaces instead of just the single one (Pi-hole DNS runs on all interfaces/addresses rather than just eth0) and someone pointed me to a similar complaint/solution (Make pihole-FTL bind only on certain IPs [v4.0] - #6 by deHakkelaar) - but I haven't tried it on v5 yet. Honestly it didn't occur to me to re-try this solution, any v5 exports know if this will work?
That worked from that point until recently with the v5 upgrade. I'll have to scrub through my history or re-attempt searches to see if I can find links I've already clicked on but after the v5 upgrade I stumbled upon using this command - pihole -a interface all - which was referenced as being a toggle to the UI's 'listen on all/single' function that wasn't quite working right, and that was great and everything was hunky dory for a while, then I patch further into v5 and it seems to have borked itself again.