Tight Layover in Lisbon

Is this a single ticket journey and that is the transfer time the airline provided, or a DIY 2 flight schedule you put together?

If the former, its a no dilly-dally transfer ( I would use the loo on the plane just before arrival to not have to waste time on the ground). If the latter, that is a high risk plan

Assuming it's all on one ticket, consider what happens if you miss your connection. Yes, they'll put you on the next available flight, but when exactly is that? If their next available flight isn't until the next day, would that cause a chain-reaction of missing other things (eg, are you supposed to get on a cruise ship the next morning? Catch a train? Start a tour?).

In addition to the great comments above, I believe you will have to go through immigration (but not customs unless you're exiting) when you land in Portugal as your first entry point into Schengen, before transferring to second flight to Venice. If I needed to be somewhere in Venice that evening, or would forfeit the cost of a hotel, I would change the flight & allow at least 2.5 hours. I read elsewhere on the forum that TAP has a free stopover in Lisbon, which is a REALLY nice city. Seems easy enough to change flights on TAP, but may effect pricing. Good luck! https://www.flytap.com/en-us/manage-booking/view-or-change-booking

Clearing immigration in Lisbon is notoriously slow. And Murphy’s Law dictates that if you have a tight connection you’ll end up deplaning at a Remote stand, taking a bus to the terminal.

Rumor has it they may have e-gates up and running that Americans can use — so look for those. Otherwise, you may have to shout and wave to get brought to the front of the line.