Version 1.4+8.20-1 of coq-mtac2 is marked for autoremoval from testing on Thu 13 Aug 2026. It depends (transitively) on aflplusplus, affected by #1141089. You should try to prevent the removal by fixing these RC bugs.
A new upstream version is available: 1.4-coq9.0high
A new upstream version 1.4-coq9.0 is available, you should consider packaging it.