How much walking on Rome, Florence, Venice Tour?

Welcome to the forum, superdub -
While you're waiting for firsthand feedback, here's what the tour description states:

Activity Level: This is one of our most active tours! Most days are
strenuously paced with 2–8 miles of walking, including hilly terrain
and lots of stairs.

I haven't taken the tour but have been to these 3 cities and can confirm that sightseeing them all can easily involve that amount of time/distances on one's feet + having to manage lots of stairs.

We did this tour pre- covid, and yes there is a lot of walking, and standing, as one tours the various museums and churches. You could opt out of selected tours. Venice, for instance, is charming just wandering and sitting along a canal with a glass of wine. Perhaps call the RS office, as revisions have been made to the itineraries. Wishing you pleasant travels, whatever you decide.

I did this tour about ten years ago and loved it, but the itinerary has changed due to rule changes at some of the big sights like the colosseum and the Vatican where large tour groups are no longer allowed. This may make it less strenuous because those large, crowded sights require a lot of standing and walking with no place to sit down. Venice is flat, except for the many small bridges you may cross, and I found Florence mostly the same except for the voluntary hill and stair climbing I did. A lot of the walking I did in Rome was also voluntary. My guess is that the walking tours of each city will be about two hours with lots of stopping for explanations. I’ve done both the Greece and Turkey tours, and found them far more active with a lot of hills and stairs. On my own in Venice I walked in excess of 20,000 steps a day, but the tour didn’t come close to this. Cobblestones are a real problem for bad ankles, but you shouldn’t really encounter too much of that in these three places. I badly sprained my ankle last year, and if I’m going to be doing a lot of hills and stairs I still put a brace on it. Going up isn’t a problem, but going down can be.

The museums have benches for sitting and cafes to take a break and have refreshments. I took this tour in 2022 at 76 years old without any problems. As remarked opting out of optional tour items is available.

My wife and I took this tour in March. There is a lot of walking especially in Venice since they are no cars. Our stay in Florence was across the river from the tourist areas, so that walk is 1/2 mile minimum RT. The Rome Hotel was up on a hill that took a little time to climb. The city walking tours can be Easy 10,000 steps. You do have half the day free most of the time to do your own thing. The museums have a lot of stairs but many have lifts that you can take.
I hope my description doesn't make you not want to go. This was our first RS tour and it was one of the best vacations my wife and ever went on. But there is some walking involved.

Although this won’t work for Venice, you can always get a taxi back to your hotel from wherever your tour day ends. I expect your guide can help you with that.

Consider stairs also. When I took the tour, we climbed the Spanish Steps to walk back up the hill to the hotel. In Florence we climbed the stairs in the Ufizzi. Venice is mostly on the flat with the exception of the bridges. You’ll need to be able to get on and off of a boat. Also, the Rome Metro involves stairs.

Likewise, as said above, I don’t want to discourage you, but you may wish to touch base with the RS office for specific questions.