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?
Yes, you do. Unless you are developing an app just for your friends, or you expect everyone not on a custom ROM to go through the ridiculous "advanced flow".
In addition to the advanced flow we’re building free, limited distribution accounts for students and hobbyists. This allows you to share apps with a small group (up to 20 devices) without needing to provide a government-issued ID or pay a registration fee. This ensures Android remains an open platform for learning and experimentation while maintaining robust protections for the broader community.
The above is from the official update by Google.