I recently went on a binge installing all kinds of roms including LineageOS 17 which has Android 10 base. All of them are no good on my OnePlus 3 and cause the problem eyestrain.
One thing to consider is that for a fresh start with this phone, you can always download MsmDownloadTool from xdadevelopers to bring OP3 to Android 7.0 eyestrain-free version. This tool completely resets your phone to factory (including relocking the bootloader) if you messed it up in any way and is probably a good way for a clean start to move on from. Then installing Paranoid Android on that is really optional.
Secondly, Paranoid Android will install but modem will not work, unless Oxygen OS 5 (Android 8) has been flashed just previously and then wiped. Have no clue why this is. I can download modem + firmware files for the OP3 based on OOS 4 (Android 7), flash it, and then Flash PA and the modem won't work, which makes no sense at all.
If anyone wants to try that procedure I can give you the file names and checksums and what not.
Personally I want to try the OnePlus 3T as it has a bigger battery and is sightly newer so used units on the market should have a fresher battery.
For me the OnePlus 3 relaxing experience isn't something that takes a long time to see. If you don't notice the difference switching to Android 7.0 or Paranoid 7.1.2 within.. almost immediately.. then I don't think it will work for you.
Actually, I would encourage anyone to download MsmDownloadTool, get it back to 7.0 automatically with this magic tool, then it will already be in a good firmware state as regarding eyestrain. If that's good, then go to the effort of trying Paranoid Android. There is no magic to Paranoid Android except the developer left out something and allowed us to get a slightly higher version without introducing the mysterious eye strain inducing change.
Not that Paranoid Android 7.1.2 is secure or anything, for sure it's getting long in the tooth, but this is discussed earlier in the thread.