There are no connection limits as such, but there are some practical limits imposed by port selection, as outlined in the man page for NFS:
NFS clients usually communicate with NFS servers via network sockets.
Each end of a socket is assigned a port value, which is simply a
number between 1 and 65535 that distinguishes socket endpoints at the
same IP address. A socket is uniquely defined by a tuple that includes
the transport protocol (TCP or UDP) and the port values and IP
addresses of both endpoints.
The NFS client can choose any source
port value for its sockets, but usually chooses a privileged port. A
privileged port is a port value less than 1024. Only a process with
root privileges may create a socket with a privileged source port.
The exact range of privileged source ports that can be chosen is set
by a pair of sysctls to avoid choosing a well-known port, such as the
port used by ssh. This means the number of source ports available for
the NFS client, and therefore the number of socket connections that
can be used at the same time, is practically limited to only a few