No fast trains between Milano C. And Verona Porta Nuova July 31-August 26?

Don't the Italian train lines have their schedule adjustment in early June? That may be why you aren't seeing the full listing of all the trains for your dates

That is not the reason, because there are regular schedules for dates in September. Also, the June schedule adjustment mainly affect Regional trains. Here, The Regionale trains are sill on the schedule for this route all through July. It is the fast trains that are missing.

If you are looking far in the future and not seeing what you expect then indeed schedules have not been published yet. There can be all kinds of reasons for that. Just wait a bit. September is still faaaaaaaaaar away.

Well I don’t see how “too far out” answers the question, when there are fast trains back on the schedule in September. I looked at the dates snd schedules and see exactly what Lola said—- a big gap with no fast trains on the schedule for those dates in August, but fast trains back in the schedule in September.

For Italo this means NO trains at all for those dates. Their schedule is empty. But full again in September.

Look for yourself— on Italy look for a train from Milan to Verona on a date like August 6. Big message says “ there are not available trains for the selected date” and below that a calendar for the week showing “not available” for every day. Then tray Sept 3 and you will see trains listed for every day that week, beginning late August.

Doesn’t anyone else find that big gap strange?

There has to be some reason other than “you are looking too far out” when there are trains on the schedule in September, but not in August.

Doesn’t anyone else find that big gap strange?
There has to be some reason other than “you are looking too far out” when there are trains on the schedule in September, but not in August.

A typical reason for this is engineering works that are not fully planned yet. They know they'll be works in August, but they don't know exactly when yet, so they can't finalize the schedule yet.
I am not finding any works notice beyond May, so I don't know what could be going on, but I do think that "wait and see" is the right approach here. After all, they are building a high speed line from Brescia to Verona, so works are likely.

and Trenitalia offers only EC and Regionale trains.

Even the EC trains are marked "Seats sold out on Train 311. Solution not saleable. Travel solution temporarily not available for the selected date."

Regional trains are showing, and they are only 39 minutes slower than the fast trains, mainly because they make more stops.

The other thing weighing against the “too far out” explanation is that it is only this route, between Milano Centrale and Verona, that has this big gap in fast train service, on both Trenitalia and Italo.

Other routes, like Milan to Firenze, have normal schedules through August and into September. At least all the ones I checked.

Even the EC trains are marked "Seats sold out on Train 311. Solution
not saleable

The EC trains are run with SBB trainsets, and SBB has the habit of scheduling trains for a whole year, no matter what. In Switzerland train tickets are for a route, not a train, so you can sell tickets even if the schedule isn't final yet. But since reservations are mandatory the system will try to find seats for you, and fail to do so, and the error messages that get thrown up in that case are not very helpful.

Personally I think the problem is probably engineering work somewhere else than Milano to Verona. That would affect long distance trains (most run Torino - Milano - Venezia) but not local trains, and may explain what you are seeing. A quick check shows that Milano - Venezia is not up yet either.