Florence is the obvious "bridging stop" on your way from Venice to Rome I'd say. Assuming you will ditch Verona which is a nice spot, but Florence is on most people's "must see" list.
I have to say I found Florence a bit meh TBH. OK the Duomo and the bridge and the museums and the galleries, and the vibe were great, but it was super crowded and that was in February, not during half term either! I felt I was being airlifted through the narrow streets there were so many people in tour groups, and wandering, and so on. But then again so was I ha ha! Great to see, but be prepared for massive crowds which I found much more offputting than the Venice gangs. 😊But that's just my opinion.
I liked Siena, which is South of Florence though. And much preferred Lucca to Florence, charming town/city but it is out of your way for getting to Roma from Venice.
If you like your food, then I cannot recommend Bologna enough. It is a kind of mad place, very lively vibe to it, loads of restaurants, and it just is well, a bit different I found.
Funnily enough I haven't made it to Rome yet, much to my amazement. But I want a whole week there and to go to Ostia Antica aswell. I wanted to get my other bucket list Italian places ticked off first and leave Rome till last. I echo the Lakes especially Garda, if that is what would interest you, but I get the feeling that you want to see the cities first.