largely depends on whether the operation and maintenance staff and developers have a high level of redis or mongo .

redis is based on memory, so it is fast enough, because the amount of data in session is small and the access is quite frequent, so it is recommended to use redis,. On the contrary, if the amount of data is very large, you can consider mongodb

I think there is no special difference, both are fine. Note that when memory is large enough, MongoDB also uses memory to buffer all data. Just consider it in terms of the team's ability and complexity of operation and maintenance.