I host some instances with Postgres and i can confirm it is compatible and it gives some performance improvement.
Also tested php-fpm and nginx and there are no compatibility issues.
When using S3 object storage as primary storage (not advisable because some occ functions does not work and migrating users data is a hell) the best solution i found was Nginx + Postgres + Redis.
During my 18 months of working mostly with Nextcoud installation and maintenance i realised that a lot of combinations can be used but there is no universal solution because it depends a lot on usecase and hardware where the software is gonna run.