If you’re brand new to IF, start with 12:12 or 14:10. Then, after a week or so, move to 16:8 and do that for a week or two, then move to 18:6 or 20:4 and do that for a few weeks. Then move to OMAD.
Alternatively, you can work OMAD in a 1-2 days a week and do a standard fast the rest of the week. For example: 5 days 16:8, 2 days OMAD.
I suggest being successful with 16:8 first. After being comfortable with that, consider moving to 18:6. Then 20:4. Then OMAD. During this ramp up time, you are training your body to be less sensitive to insulin.