The size limit for the group depends on whether you have an active Full Platform Access subscription.
Without Full Platform Access
Users without Full Platform Access can connect with up to 10 people on the platform, meaning the maximum number of members in a group is also 10.
With Full Platform Access
Group admins and managers who have an active Full Platform Access subscription do not have any limits on the size or the number of groups they can create.
Note: If you want to know how to get Full Platform Access, check the article here.