Thanks for the response.
On iOS I’m using safari, and I’m pretty sure it doesn’t have any auto deleting options unless I’m mistaken.
I just tried Instagram (I know, I know) and this forum, logging in using normal safari browsing windows on my iPad. Also had safari remember the login details.
I do have lockdown mode enabled. Not sure if that would impact anything.
I’m actually still logged on in safari where I created the Home Screen shortcut. In both cases as soon as I open the pwa it opens in a new window but isn’t logged in.
I’m assuming this forum is a pwa? Sorry I haven’t been able to find much information to know whether something is a pwa or just a bookmark.
** edit: grammar