Home screen installed PWAs are treated as a separate web browser. For all web browsers, content is only deleted after 7 days in which you use that browser. So

Home screen installed PWAs are treated as a separate web browser. For all web browsers, content is only deleted after 7 days in which you use that browser. So if you shut for phone off for a month, and then turn it on, and open safari, that whole month only counts as one day, since you did not use the safari browser during that month. The same rules apply to PWAs installed to the home screen, which are being treated as seperate browsers. Of course, the count of days of use of this "browser" without using the main site will always remain zero. But for third party cookies, or third party content from an iframe that uses local storage, those would get nuked if the home screen installed PWA is used on 7 different days without interacting with those domains.