Athens to Thessaloniki itinerary suggestions - first visit

How fast do you typically like to move? My own bias is sloth-like, so I'd have a hard time fitting all of that into one trip. I spent ten days in the Peloponnese, and I had planned a ten-day loop out of Thessaloniki that got scuttled by covid.
To start sorting out your own preference, I would work backward and first decide how much time you would like to spend in Thessaloniki. I admittedly was going to give it short shrift--even though it is a fascinating city--because my trip was more nature/small-town focused. You could certainly fill a couple days.
Delphi could be a night or just a stopover given your time constraints. Meteora I would want two nights to have one full day.
So, you could have a tight trip and fit it all in, or you can save something for a return trip. I was going to include My Olympus and Pelion peninsula in my trip to the north. If you saved the Peloponnese, you could look at other options.

I have not been to most of the places you mentioned, but my friends told me that Thessaloniki is not that scenic. So, don't budget too much time there.

Well a good deal of it was burned to the ground, Bark. We have no idea if Elena has any interest in history or scenery or what.

Thank you for your replies! Sorry for not providing more details. We are interested both in history and scenery. Can we split it down the middle? Where to stay in Nafplio and Thessaloniki? Good restaurants, not too touristy?

Elena

I am not sure if I understand the question. What have you decided to do? Did you research Thessaloniki and decide to stay there a few days?
You might want to sort out where you will drop the car--Theassaloniki did not look like a fun place to drive particularly. I'd consult a city guide, as I never got there--but it looked like there were tons of bars and restaurants of all types.
In Nafplio, we knew we would be taking day trips out of town and we prefer to have a view, so we stayed outside of old town up the hill at Sunday apartments (run by a nice family). It was easy parking, easy to get out of town, and we never minded walking down to old town for dinner. https://sundayapartments.gr/
There is a recent thread here about restaurants.

We've been to Thessaloniki 4 times - we just really like the city. Walking along the waterfront is great, the Archeological Museum, the statues of Alexander the Great and Aristotle - it just depend on what you like to do when you travel. Our favorite hotel is the Electra Palace - right in the center of the city near the waterfront.

We also visited Nafplio this past April and it feels to us like it's lost some of it's charm. It is however, a good base for visiting Tiryns, Mycenae, Epidaurus and Nemea.

We are planning to stay in Thessaloniki a full day and will book the Electra Palace. I love walking in the city so look forward to visiting Thessaloniki. Thank you!