Starting in August, installing APKs from unverified developers will require a new procedure called Advanced Flow. It involves enabling developer mode, rebooting the device, and waiting 24 hours with biometric verification.
After that, you choose: allow the APK installation for 7 days or indefinitely. The procedure is a one-time process and applies to all versions of Android.
Will the 24-hour wait stop you from installing APKs outside the store?
From what I'm reading it sounds like it is not per-app:
Once you confirm you understand the risks, you’re all set to install apps from unverified developers, with the option of enabling for 7 days or indefinitely. For safety, you’ll still see a warning that the app is from an unverified developer, but you can just tap “Install Anyway.”
https://android-developers.googleblog.com/2026/03/android-developer-verification.html
Not that this makes it ok, this process is still something the vast majority of users will not do in practice and will kill the viability of apps with developers unwilling to show ID to Google.