I agree it should be fine (unless things go wrong).

FWIW I’ll mention that we flew into Lisbon on a day the immigration workers were on strike and we just barely missed our connection and we ended up renting a car to drive to Seville because the travel time was a little better than waiting for the next flight.

90 minutes should be fine assuming your incoming flight is on time or max 20 minutes late. It's the same terminal, so no waiting for a bus or train. You will walk to passport control, then walk to your second gate, there is no security check since you are arriving from a US flight. The line at passport control is your biggest issue/worry, but normally it should be 10-15 minutes.

Would you have the option of getting on the flight 5 hours later if you missed the earlier connection? If so, I would feel comfortable booking this.

Trying to book flights to Spain this summer and the choices for our dates seem to be a 90min layover in Lisbon or 7hrs. We would have lounge access, but it will be middle of the night/early morning so not exactly jump up and see the city and come back hours. Traveling with two kids, teen and elementary school age. Would much rather do the 90 min layover but worried about losing a day of travel if we miss our connection. Any experience with this?