The phrase "limited functionality" means that something is not capable of doing everything it should or could do. It refers to a restricted or reduced level of performance or features. Full definition
This would also be an early version with limited functionality. (windowslatest.com)
It's a tool used by a lot of hackers and bad actors to steal data or passwords, so that sort of limits the functionality of this website. (lincolncole.net)
This had reasonable success, but was a fairly small system with very limited functionality, and was actually a very large investment in terms of development and the associated infrastructure. (ftgames.com)