I solved this problem at my university (not Eduroam) by installing a CA certificate in Android (8). It then becomes a choice in the CA Certificate menu and you can sign in.
Hopefully, you can find out from the IT people where is the CA Certificate to download to your Android.
I think choosing "Don't validate" is unwise, and that's actually what many university IT web sites advise (Google finds the instructions easily).
Edit: for Eduroam, there's an app that reportedly solves the problem for Android 8.