Just to highlight as this often gets misreported when this is raised.
You will still be able to install unsigned APKs, but the first-time procedure to unlock the ability will include a 24 hour wait. After that, unsigned APKs can still be installed as usual
And APKs outside of the Play store can still be distributed unsigned, subject to the 24 hour wait for Play Protect devices
Honestly, I'm less concerned with the initial wait and more concerned about how this is run entirely through Google Play Services, leaving Google with the ability to alter the deal next time they have another benevolent security decree.
You will still be able to install unsigned APKs, but the first-time procedure to unlock the ability will include a 24 hour wait. After that, unsigned APKs can still be installed as usual
And APKs outside of the Play store can still be distributed unsigned, subject to the 24 hour wait for Play Protect devices