Hi, leb717,
I can't vouch for Edinburgh, as I try to avoid it, but I can tell you that many of the restaurants along the river in Inverness have outdoor seating. Most of them are along the west bank of the river, along Ness Walk, although I think that Johnny Foxes, at the corner of Bridge Street and Castle Road, also has an outdoor seating area. Check the menus before you decide, as Rocpool is very expensive.
The Eden Court Theatre had a series of outdoor dinner concerts called "Under Canvas," or something like that. They may be done by early September.
Cafe Sia, in Broadford, has an outdoor seating area. Their food is usually very good and reasonably priced. They've had to offer a limited menu, however, due to Covid and staff shortages. Of the three areas that you've mentioned, this is the only one where midges could be a problem.
If you don't mind getting a little messy, the Siaway takeaway restaurant, also in Broadford, does excellent fish and chips. If you're going for the fish supper, get the battered haddock, not the breaded. Then you can do as the locals (and tourists) do, enjoy your meal on the benches along Broadford Bay. Or if the midges and/or weather are not conducive to outdoor eating, you can enjoy your meal from the comfort of your car.
I hope that you have a great time in Scotland!
Best wishes,
Mike (Auchterless)