For MongoDB data directories only XFS is recommended. The ext4 filesystem isnt so bad but when there are a very, very high number of random accesses (which WiredTiger can reach) it can hit a bottleneck. To be fair most deployments will never hit this bottleneck, but it does remain an official production recommendation of MongoDB [&]

https://www.percona.com/blog/2021/02/15/bare-systemd-method-to-create-an-xfs-mount/