Advice for itenerary in July (Italy)

I think it’s probably Ok
Enough time in each location but it’s easier to see big picture if you count your trip in NIGHTS not days
Does 5 days in Florence mean 5 nights in Florence, for example? Because 5 nights is really just 4.5 days once you check out, travel to, check in, get oriented.

I would give Rome another night/ full day

Days are adequate for all.
5 days in Florence gives you also the chance to take some day trips. Most people don't visit Florence more than 3 or 4 nights.
I want to warn you that Florence is a hot oven in July, so make sure you choose your accommodations wisely as you will need plenty of A/C and, if you can afford the splurge, a swimming pool would not be a bad idea (although very few hotels have a pool downtown Florence, and they are not the cheap ones).
There isn't a lot of difference in temperatures between North and Central Italy. Proximity to bodies of water (sea, lakes) or high altitude (mountains) are the factors that make the difference (somewhat) in temperatures, not much latitude.

Thank you for your reply, 4 days = 5 nights, 4.5 full days, and 5 days = 6 nights, 5.5 full days.

I plan to visit Pisa, Lucca, and Siena while staying in Florence. In that case, is 5 days okay or you would suggest me to cut some off? I cannot afford a pool but I found some airbnb with ACs.

I wonder whether you considered doing some of your hiking in the Dolomites? The weather should be much, much milder there (at altitude) than elsewhere in Italy. I'd be inclined to drop Sorrento and spend the time (plus maybe one of the Lake Como days) in a place like Ortisei.

I suggest the above as someone who ran, screaming, to the Dolomites back in 2015 after having spent June and the first half of July in Rome, Orvieto, Sicily, Puglia, Bologna and Padua.

Take a day off Florence and CT and add to Rome.

Because Florence sits in a sort of bowl between hills, it holds in the heat.
If you are not used to high humidity, I would avoid the more mid and southern parts of Italy and stick to the north, and make sure to be near lakes or accommodations with pools.
I've been in Florence in early June, and couldn't leave the apartment with AC during the day because of the heat and humidity.
It depends what you are used to at home, but now I just go to Italy late September to avoid that type of weather.

Since you plan multiple day trips from Florence I wouldn’t cut anything to your Florence days. Florence needs, at the very minimum, two full days (dawn to night), and that is just to cover the top attractions. You will need a full busy day to see Lucca and Pisa (on the same day) and another day for Siena. You can use your 5th available day to see more of Florence or add one more day trip (Arezzo, Cortona, Pistoia, San Gimignano, Chianti Hills, Volterra, Fiesole, and many more to choose from).