muhomorr exactly what I originally reported! From my logs, I saw that many apps were constantly being killed due to running out of memory. But didn't try to disable the secure app spawning feature.
Clearing the cache of system ui and the launcher improved a bit the situation, but this makes the performance come back completely as in previous releases. By the way, after the reboot I got another round of app optimization with just 10 apps this time. It finished quite fast and it asked to restart apps.
If this is indeed an upstream issue, as many reports suggest, then the GrapheneOS feature secure app spawning triggers this issue and makes it much worse for some of us. Perhaps it's some installed apps, or something else. In any case, based on the number of comments in this post compared to other release posts, I think this is an issue affecting not such a small number of users as claimed above by the official GrapheneOS account, and perhaps devs should try to reproduce the issue and look into a possible solution.