Squinting itself is not bad for your eyes and when you do squint it will not harm your eyes.
However when you do need to squint to see it usually means that you're having some vision loss and are unable to see things up close like you used too.
So if you need to squint it's a sign you might need to wear glasses or contacts.
Another reason you may need to squint is because of cataracts which can be corrected through cataract surgery.
So if you are needing to squint you should make an appointment with an eye doctor and have your eyes checked out.
Because you should not need to squint to be able to properly see.