persophecles
Are the builds for the security previews available? I can not seem to find them.
Yes, they're available. They're not currently listed on the releases page to avoid cluttering it and having to explain the difference there. They're the same URLs as the regular releases with the build number incremented by 1 so it's easy to get the URLs for downloads if you want them.
I root my phone so that I can use Adaway and Tasker, but after the 2025100901 update, I can not root it with Magisk. If the security preview builds are not available, is there a way to roll back to the last stable build?
This means you aren't using GrapheneOS but rather a derivative of it with the core OS partially replaced with something else and have a massive portion of the security model compromised. AdAway uses an improper approach to implementing DNS filtering based on the legacy hosts file instead of doing it properly. The approach they use is very slow, does not provide you with information on what's being blocked and requires breaking the security model of the OS. The app is insecure and not correctly implemented. It's always wrong to use root access to implement something like this instead of doing it properly following the principle of least privilege. The same applies to Tasker. If these were safe and secure, they would only require the permissions they actually use rather than full access to everything and compromising the OS security model in a severe way to obtain it.