Comcast only changes my IP once every 2-3 years. I just manually update it. But zoneedit does have a free dyndns endpoint if your IP does change often.
Yes, I leave my computer on 24/7/365. The webserver/my primary desktop is on a Core2Duo build from 2007 and it still chugging along just fine.
I copied the boot and OS partitions to a SSD and swapped it in in 2018. It's nice enough. This machine actually has something like 25TB storage total. I'll probably have to swap that 2018 SDD out soon since SSD don't have indefinite lifespans like the occasional lucky HDD.
I have plenty of newer computers in the shared keyboard/mouse span of monitors in my array of desktop computers. It's just that they run newer software and newer software is worse software. Things have been mostly downhill in linux UI since "convergence" with mobile, IBM/Red Hat's dumbing down of Gtk, and the take-over of containers over actually running applications on your OS.
Try copying a file path to clipboard then using a Gtk3/4 program and opening a File->Open dialog and pasting the file path in. There'll be no text-input area there to paste in to and it will give an error. https://gitlab.gnome.org/GNOME/gtk/-/issues/5872 This has been a known issue since they caused it in 2014 by removing the gsettings to allow for having text entry bars.
How does the DNS thing work? They use a DynDNS client on your computer or what