I’ve noticed the same slowness on PostgreSQL 12 and PostgreSQL 13 and i can confirm that setting jit = off makes the reports to load up faster again. Thanks for sharing this information.
Note: My previous comment / text was wrong, jit = off is still required for PostgreSQL 13
this solution seems to work for the latest as well - I am using GVM 21.4 and Postgres14.
Had similar issues postgres was at 100%cpu and the task eventually stopped (interrupted)
Now changed the setting to jit=off and openvas are the processes with cpu (not postgres)