Phones are generally seen as more secure because they're less likely to have malware and the apps should be running in their own sandbox, meaning it's more difficult to see what each app is doing and so theoretically it's more secure.
Most desktop operating systems do not have sandboxing in place, have known malware that could be installed much easier than on a phone, and harder to verify that the system is secure. This is doubly so taking into account that basically the only way to use the banking information is through a web browser, which could have any number of junky web extensions installed.
While things are incrementally changing on the desktop front (mostly on Linux with Atomic distros, Flatpak/Snap, and Firefox container tabs), most banks are only familiar with Windows and macos, and since those two have the most security risks, they'd rather play it safe with the relatively more standardized, theoretically more secure phone OS.
I've started having issues recently, too. After a work injury, I finally saw my GP, who recommended Physical Therapy, which has basically just been a guided workout with some yoga moves worked in over the course of an hour.
It hasn't fixed my pain yet, but it's made it better, and my pain was explained in a way that makes sense (my shoulders and core weren't as strong as they should have been, placing undue burden on some of my backmuscles).
If you don't want to go to PT, I'd strongly recommend just slowly doing 10-15 minutes of simple stretching like what you might have done in Gym as a kid. Stretch to the point of mild discomfort, not pain, doing each stretch 3 tines for 10 seconds. It might be worth looking into some basic yoga poses that target your particular pains (or the ones that you want to target first).
I'll bet you'll notice good results after a week. If not, definitely go see your GP again.
Obligatory "I am not a doctor"