What is the MX model?
VPN users count as active connected users, so it has to be based on the maximum number of clients supported by each model.
For example, if the MX supports 50 clients, if you have 30 clients connected locally plus 5 connected via VPN Client, this means that you have 35 clients connected simultaneously, that is, theoretically you will still be able to connect another 15 VPN clients without problems.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.