Only 2 days in Lisbon

The Jeronimos Monastery, https://www.lisbon.net/jeronimos-monastery, and afterwards, a Pasteis de Belem, https://pasteisdebelem.pt/en/. Once I find my itinerary I can tell you where we listened to Fado.

Edit: Here's where we had dinner and listened to Fado, https://www.casadelinhares.com/. The music was excellent, performed by professional musicians. I don't know whether you would consider it touristy. Most of the patrons were Portuguese who knew their Fado.

The monastery is beautiful but getting to and from Belem and seeing the sights there is a bit of a schelp to a suburb, and crowds can make the tram unpleasant. I'd only go if your group has a lot of energy and is willing to get up early and have a long day, because just taking in the sights of walking in Lisbon (see Rick Steve's 3 different neighborhood walks in Lisbon) is a full day, really, and shouldn't be missed.

Don't wait in line for a Pastel de nata in Belem unless you're really into food history - equally good versions can be found all around Lisbon and Portugal and you may find you don't care for the pastry anyway - my husband didn't. Anyway most people think Manteigaria in Baxia is just as good if not better than the ones from Belem and it's a lot more convenient.

I really enjoyed doing this food tour which pretty much doubled as a Baxia neighborhood walk. There's loads of food tours, and that can be a good way to learn about and see the city while getting context - the only problem is there was so much food it ruined my dinner plans. But that might work for you if you wanted to go to one of the less touristy Fado bars that don't require you spending money on mediocre food. We didn't do any Fado activities so I don't have any personal recommendations there.

If you like museums, the Gulbenkian is a must and the tile museum is also interesting. The aquarium is absolutely awesome.

I really enjoyed my visit to Lisbon. Depending on how much you like churches, I found the Church of St. Dominic a "must" for me. I am not an overly religious person, but when I walked into St. Dominic, I was moved to silence and contemplation. It is really a lovely church to just go sit inside and look around for a bit. Wouldn't take a lot of time and isn't far from the area you are staying in.

Also, just throwing in a comment about food. In the Barrio Alto neighborhood, my wife and I stumble across Manny's Place (https://www.mannysplacelisbon.com/). It is just a small place on a corner, but the food was fantastic and Manny was great.

We also had a short layover in Lisbon and we left not seeing and doing as much as we liked. But it's good to leave a special place wanting to go back:)
We also stayed in Baixa which is centrally located. The first night we did an Airbnb experience and went on a sailboat tour of the river Tejo which allowed us to float by and see the city from a different perspective. From the river you can really see the 7 hills of Lisbon, sail under the beautiful red bridge and then return to port.
The next day we did another Airbnb tour to Sintra which took time from exploring Lisbon but it was worth it! Sintra is like walking into a fairy tale book. After a quick rest, we had dinner and walked through Alfalma which I highly recommend doing at night. It is even more charming at night and the miradours, or viewpoints, in the district take your breath away.
The next morning we took an Uber to Belem, which is about 20 minutes away. We did not go into the Monasterio Jeronimo but saw the Belem tower and the Belem monument. The green space in that area was lovely.
We then had our Uber driver take us to the Carmo Convent which we toured and then explored the Chiado neighborhood. We walked back to Baixa after that for some rest in our apartment. Later that evening we met up with my cousin who lives near Lisbon and we didn't get to see as much as we would have liked that evening due to all the catching up with family.
It's possible to get a "taste" in 2 days but it will be a packed schedule if you can manage it.
There's an app called "Visit a City" and you can choose different itineraries based on the amount of time you have. You can even choose if you want to see the sites at a leisurely pace or a quick pace. Enjoy!

We spent one day visiting the Castelo De S. Jorge and then exploring Alfama, partially following the Rick Steves walking tour. The Alfama is the oldest neighborhood in Lisbon; it was not destroyed during the earthquake of 1755. That day we also visited Mosteiro De Sao Vicente De Fora. We walked there from Alfama. So it's doable in one day. The monastery is filled with gorgeous blue and white tiles, and there are stunning views of Lisbon and the river from the rooftop terrace. It was one of our favorite days in Lisbon.

Visiting Belem is worthwhile, too. Also just wandering the other neighborhoods in Lisbon and enjoying views and drinks from the miradouros.

If you like museums, I agree with the poster who recommends the Gulbenkian Museum.

For me,the Discovery monument and the Aquarium.