Whether you can work off-campus, and how many hours, depends on the conditions on your current (extended) study permit, not just the fact that you're a full-time student.
Historical note (time-bound): IRCC's standard rule was a 20-hour-per-week cap on off-campus work during study terms. In mid-November 2022, IRCC temporarily removed the 20-hour cap for eligible students, allowing full-time off-campus work while classes were in session. This was a temporary policy that has changed since — always check the current IRCC webpage for the policy in effect on the date you're reading this, rather than relying on this thread's date.
What to actually do:
- Read the conditions section of your extended study permit — it will state directly whether off-campus work is authorized.
- Check the current IRCC study permit webpage for whether the 20-hour cap (or its removal) is in effect for your situation, since this rule has changed more than once.
- If your permit doesn't clearly authorize off-campus work, don't assume it does just because your previous permit did.