I am facing same issue on iOS 14.6, From a hybrid Cordova app,
OIDC authentication URL is opened in SFSafariViewController, up on successfull login session cookie is
set by the server.
Applicaiton is dismissing SFSVC view and authentication is code is passed to hybrid app for validation.
Next time (within few minutes or less that a minute) when SFSafariViewController is opened with OIDC URL, previously set session
cookie is missing (Session is needed for a customer context switch case within App for the same logged in user)
This issue is happening for few of the customers only, issues are getting reported as soon as they took 14.6 OS upgrade.
Few case were blocked for few days, un-install -> install helped few people, but again it failing for them.
Seems something related to cookie handling in WebKit after 14.6 OS security changes