You are obligated to collect (or at least attempt to collect) anything the insurance applied to the deductible and/or co-insurance.
Then the rest is a policy issue. You may choose to accept the insurance approved amount (very different than paid amount) even if you are out of network. You may choose to balance bill to your full amount provided the patient was aware of your non-participation. You may choose to treat the patient as self pay, and require payment at the time of visit and supply paperwork for the patient to submit on their own to insurance.
Example:
Bill $300 for 99214. Insurance approves $180, then applies $100 toward deductible, and pays at 70/30 of remaining $80, so $56. The insurance applied $100 toward deductible, and $24 to co-insurance. You must bill the patient $124 so your total payment is the approved $180. The remaining $120 is an office policy decision. You may only waive deductible/co-insurance if the patient meets financial hardship (another office policy decision).
From my experience, most offices do not balance bill. It's also a good idea to have the patient sign something prior to treatment acknowledging they are aware your clinician is not participating. Many states have a No Surprise Bill act which prohibits balance billing for emergencies and situations where the patient cannot choose a clinician (think anesthesia, pathology, etc.), which does not apply when a patient knowingly elects to receive non-emergency out of network services.