This app was mentioned in 11 comments, with an average of 1.27 upvotes
https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger&hl=en
Used it to reduce the resolution on my HTC 10 to 1080p, since I don't think a 5.2" device requires a 1440p screen.
Maybe try a dpi changer to reset the resolution/dpi
https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger
Whilst I've had the problem of the touch area not matching the screen it was only on the stock Camera and after tweaking the resolution and didn't appear to affect anything else.
If that doesn't work then maybe reload the stock ROM (available from Sammobile) through Odin and start again.
I'm currently using TWRP 3.2.1 downloaded through the TWRP App:
https://play.google.com/store/apps/details?id=me.twrp.twrpapp
I use Easy Dpi Changer You will need root for it You'll probably want to use a dpi calculator like this for the Dpi part
You could just buy an old device and use that.
Anymore they're cheap for used devices on eBay.
It's often better than using glitchy software tweaks.
Otherwise you could look into Easy DPI Changer [ROOT]
https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger
There may be some apps that work without root, but you will have to use ADB (Android Debug Bridge) via a PC.
I'm trying OxygenOS-team's half-finished ported Xposed about today, I hope it'll work. I've also tried some global dpi changer from google play, but it ruined my phone, I had to restore a backup. This one (https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger) seems to better though, and since it resets your dpi on reboot, I don't think it'll ruin anything - the only problem is that it's global. The third thing could be a custom patch using Lucky Patcher, but I've never tried making one, and it doesn't seem easy...
It's already QHD but you can change it if you have root https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger You can use this. I used to use it on my S9+
https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger
Change the resolution
https://play.google.com/store/apps/details?id=com.chornerman.easydpichanger
Device wide, root required.
If not rooted you can use adb.