Comment 20 for bug 1971935

Interesting, that gives me something to work on. Same happened here, and guess where rpc_pipefs is mounted in the end...

$ sudo apt install autofs -y
(...)
Not creating home directory `/var/lib/nfs'.
Created symlink /etc/systemd/system/multi-user.target.wants/nfs-client.target → /lib/systemd/system/nfs-client.target.
Created symlink /etc/systemd/system/remote-fs.target.wants/nfs-client.target → /lib/systemd/system/nfs-client.target.
auth-rpcgss-module.service is a disabled or a static unit, not starting it.
nfs-idmapd.service is a disabled or a static unit, not starting it.
nfs-utils.service is a disabled or a static unit, not starting it.
proc-fs-nfsd.mount is a disabled or a static unit, not starting it.
rpc-gssd.service is a disabled or a static unit, not starting it.
rpc-statd-notify.service is a disabled or a static unit, not starting it.
rpc-statd.service is a disabled or a static unit, not starting it.
rpc-svcgssd.service is a disabled or a static unit, not starting it.
rpc_pipefs.target is a disabled or a static unit, not starting it.
var-lib-nfs-rpc_pipefs.mount is a disabled or a static unit, not starting it.
Processing triggers for man-db (2.10.2-1) ...
Processing triggers for libc-bin (2.35-0ubuntu3) ...

$ mount -t rpc_pipefs
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw,relatime)

$ sudo systemctl status run-rpc_pipefs.mount
○ run-rpc_pipefs.mount - RPC Pipe File System
     Loaded: loaded (/run/systemd/generator/run-rpc_pipefs.mount; generated)
     Active: inactive (dead)
      Where: /run/rpc_pipefs
       What: sunrpc

$ sudo systemctl status var-lib-nfs-rpc_pipefs.mount
● var-lib-nfs-rpc_pipefs.mount - RPC Pipe File System
     Loaded: loaded (/proc/self/mountinfo; static)
     Active: active (mounted) since Tue 2022-07-05 12:45:11 UTC; 33s ago
      Where: /var/lib/nfs/rpc_pipefs
       What: sunrpc
      Tasks: 0 (limit: 1119)
     Memory: 20.0K
        CPU: 1ms
     CGroup: /system.slice/var-lib-nfs-rpc_pipefs.mount

Jul 05 12:45:11 j-autofs-nfs-common systemd[1]: Mounting RPC Pipe File System...
Jul 05 12:45:11 j-autofs-nfs-common systemd[1]: Mounted RPC Pipe File System.