I am new to opnense and I have a question to do a job
I want to limit the bandwidth differently for each user connecting through the captive portal
Example
user 1 = 1Mbts
user 2 = 512kbts
user 3 = 5 Mbts
I think you need to create multiple captive instances, 1 for each user as load balancing for Captive portal is bound to instances.
https://docs.opnsense.org/manual/how-tos/guestnet.html is guide how to setup guest network for captive portal and how to configure load balancing.
Just follow that guideline.