If you plan to vote by mail, you should check your state's .gov page to see the cut-off date your ballot has to reach the elections offices to be counted. For PA, it's October 27th. But some are saying everybody should consider it Oct. 20th instead for safety, due to mail delays.
I'm starting to get messages by phone about mail balloting, and I can't verify the authenticity of the texts, so can't respond to those, but one did give a true link to PA's Voting Information page, where I can apply for a mail ballot.