I also used to use the same thing. Been a long time since I've had to remote access someone else's PC for troubleshooting but I think I also used TeamViewer back in the day (which I assume might not work as well on Linux anymore now that Wayland is the norm?). Perhaps you could write a quick script to get your public ip address by curling some web service that tells you your public ip address, add a desktop shortcut to that script, and over the phone tell the person to double click that desktop shortcut and read out the number they see. It'd still trip up the most tech illiterate but hopefully if they're at the "can follow clear and basic instructions" level they can manage that. And possibly there are still dyndns clients that do that; I've just not messed with any of that for a long time, but you can set that up on their PC if that stuff is still around.