Check your registration -- Track your ballot
Statewide, registration closed on October 19th. If you haven't registered yet, it's too late for the 2020 election.
It's too late to safely mail your absentee or mail-in ballots; take them in by hand to your county election office - 8am until 8pm including this weekend right up through Election Day. On election day, they are open 7am to 8pm. You can't turn absentee or mail-in ballots in at your regular polling place, but you can void them there and ask to vote regularly. Be sure to bring the ballot and ALL ENVELOPES with you if you aim to try this. It's better to go to the county office in advance: 542 Forbes Avenue, Room 601, Pittsburgh 15219 if you need to talk to someone; if you're just dropping off a ballot, you can go to the lobby, and there are short-term surbside parking spots available.
If you haven't requested a mail-in or absentee ballot already it's too late to do so. You need to show up in person at your regular polling place. But if you DID request a mail-in ballot and it didn't arrive, you can go to your county elections office (above) during business hours: Monday through Friday, 8:30 AM to 4:30 PM. They will make you sign a declaration that you haven't already voted, and give you a new ballot which you can vote on the spot. This is the best option if you didn't receive your requested ballot and want to make sure that your vote counts on election day.
Drop boxes
AFAIK there are no drop boxes in Allegheny County, but you can drop off your mail-in ballot at the county elections office until 8pm on election day.
Early voting
It's too late to vote early ("in-person mail-in voting") unless you already requested a ballot before October 27th. If you did, mail-in/absentee ballot drop-off is allowed at the county elections office (542 Forbes Avenue, Pittsburgh 15219) every day 8am to 8pm through election day. If you never received your ballot, you can go in and hassle it out during business hours (M - F 8:30am - 4:30pm).