iPad 10th gen getting weird lines when written on

Good quality screen protectors, either tempered glass or plastic film, should have no impact upon the performance of an Apple Pencil. Manufacturers of good quality iPad screen protectors often back the performance of their product with a warranty. Good quality comes with an appropriate price-tag - i.e., they are not cheap.

There are many cheap/poor-quality screen protectors that cause issues with the Pencil - if they work at all.

Per your description, it is very likely that you have one of the latter.

Whether or a not a cheap screen protector is suitable for use with an Apple Pencil, or will provide adequate protection to your iPad screen, will only be discovered by experience.

Perhaps consider that your iPad screen is the single most costly component of your iPad - and will be expensive to replace if damaged. The cost of a replacement screen is substantial - and is considerably more expensive than a good quality screen protector from Zagg, Otterbox or other leading manufacturer.

Your reddit post clearly states that you are using a third-party ("knock-off") stylus and a cheap Screen Protector.

Unless you are using a genuine Apple Pencil, compatible with your iPad, performance and function will be unpredictable. As such, it is impossible to provide definitive guidance beyond substituting for known/supported hardware.

You would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad. If a fault is identified, you'll be in the best possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple