We are doing a 45 day trip to Portugal and Seville in Sept-early November. Never been before. I've driven a lot in Europe over the years including last Sept in France. Last year we took trains to all of our tour of Belgium, NL, Germany, Austria, Italy and France. I'm 84 and had no issue in Paris last Oct renting a car to Normandy. I know to check that when I book.

I started out thinking we would do trains on this trip but then thought we would see more on roads and there might not be trains in some places. Our plan is to fly into LIS and immediately go to Porto. There and for the rest of the trip we would stay approximately 1 week in each place with some side day trips. Our stops are: Porto, Coimbra, Tomar, Seville, Lagos, Lisbon. Guessing a car is not needed/wanted in Porto, Seville, or Lisbon.

Thoughts? Thanks in advance. Steve

You are correct about the cities -- cars would be a disadvantage in Porto, Seville, or Lisbon.

Whether a car would be an advantage to you would depend, I think, on exactly what side trips you envision and your patience with public transportation. You can check your transportation options using rome2rio.com
FWIW, I think getting to / from Seville might be tricky by public transportation from Portugal. I could be wrong.

If you do get a car, be sure your lodging has parking.

One question: Why fly into Lisbon if you plan to start your trip in Porto? You might have to route through Lisbon, but I'd check for multi-city (open jaw) flights into Porto and out of Lisbon, if that's your plan.

Stop over at Merida (a lot to see) at your train ride from Tomar to Sevilla.
You may also include Evora (bus) if you are interested in.

Sevilla - Lagos is a long bus ride. You may also use trains between Tavira and Lagos.

We did a 10 day trip to Portugal pre-pandemic. We saved Lisbon for the end and after returning our rental car at the airport, took an airport bus into Lisbon as we initially headed from the airport to Evora, not a long drive and a place that I highly recommend visiting. We did stay at hotels with car parking and in Porto we did use our car for day trip to Guimares. Both in Evora and years ago in Seville, the underground parking ramp was so steep, the hotel staff drove the car down and parked rather than letting my husband do it himself.

If you land at Lisbon, don't drive to Porto the same day. Train or plane

I've visited both Portugal (Porto, Guimarães, Pinhão, Coimbra, Evora, Lisbon, Sintra) and Spain (Madrid, Seville, Granada, Barcelona, Toledo) entirely by bus/train. While I'd never travel in some parts of Europe by anything other than public transport, I did feel that we might have benefited from renting a car in Portugal (outside of the cities).