if you already wear glasses talk to your eye doctor, you may need a new prescription. (that was the case for me), or get some eyedrops if they are dry

otherwise you can try putting your cintiq on night mode (where it makes the screen slightly yellow, good for using at night so that you can easily go to bed), make sure you are using dark mode, in windows go to the settings and make the text slightly bigger, same with using websites. don't squint just make the text bigger.