Limitation of the cable modem users?

There is a way to autorize and limit speed and cap data with cable modem users ?

Depends on where you want to terminate it, if on mikrotik it’s possible by standard features of Splynx,
or with Radius on some other NAS.

Any way to do it with ubiquiti hardware like ER-X ?

https://splynx.com/2061/ubiquiti-edgerouters-pppoe-radius-support/ ?