I'm wondering about whether a disposable diaper with vent holes punched or sliced in the plastic liner would be breathable enough to be a surgical mask? would this be able to protect me from covid?

No: This would be quite a site but never meet the testing requirements to equate to the N95 or KN 95 masks known to be protective. Wash your hands often or use sanitizer. Wear a simple mask that cuts down the risk of you spreading germs to others and expect others to do the same.If so you should be fine. If people have & don't wear a N95 mask properly it doesn't protect them either.