I can't think of anyone who would not come to Scotland because of the mask rule. Indeed it is more relaxed than most western European countries seem to be right now. We may not be as relaxed as England, but to suggest a mask mandate affects tourism is ridiculous. The whole world has been wearing them for 18 months, no one is going to avoid a country for a holiday because they still want you to wear one in a shop! People are just happy to get away!
The main barrier to inbound tourism was the need to isolate or the inability to travel around the UK and book accommodation. Now those have been scrapped for domestic and a huge number of foreign tourists, as well as many European countries also scrapping it for vaccinated arrivals and returning citizens, the numbers of tourists will creep up again as we get through the last few weeks of summer and the limited festival. Those of you cancelling holidays to Scotland because of a mask are free to do as you wish, but your place will quickly be taken by people who can cope with not needing to wear one for 99% of thier day. I'm hearing more and more foreign accents in Edinburgh every time I go up town and you're never very far away from an English group either, the airport and your buses gets busier each time they go past my window too, which also overlooks the increasingly busy landing path into Edinburgh airport, so quite who isn't welcome is beyond me. It's very much a case of doors opening again.
As for seperate NHS apps. Every UK nation has a different one because their relevant NHS came up with a different one. Yes it cost the tax payers, just as using the English one would have, just as everything with Covid has done. I seem to remember, back at the start of all the contract tracing apps the English one didn't actually work properly and had to have more money thrown at it to get it to function. The Scottish one, which came out shortly after, worked right away.