Is there any evidence that local storage is being used as a pseudo-cookie way of tracking users? If so, keeping local storage saved while regular cookies are being deleted would defeat the purpose of deleting cookies for anti-tracking reasons.
Yes [1].
[1] https://clearcode.cc/blog/alternatives-to-cookie-tracking/
Please read the HTML/Web Storage standard [0] and try to find where Apple is not honouring it.
Even before this move by Apple, you should already had to consider localStorage to be subjected to being wiped by actors not in your control.
On top of that, localStorage privacy concerns were also in the standard. See section 11.4.1 [1].
Nevertheless, I reckon Webkit should expose the option to the user.
I feel your pain, I really do, but I can't see how Apple made PWAs impossible.
[0] https://html.spec.whatwg.org/multipage/webstorage.html#webst... [1] https://html.spec.whatwg.org/multipage/webstorage.html#priva...