You don't get a 'visa on arrival (with a visa exemption)'. That's an oxymoron.
You can't have both at the same time and as you appear to be from one of the eligible countries , you will enter on a visa **exemption**. That means you are EXEMPT from needing a visa to enter the country, so how can you also have a 'visa on arrival'??
Those are only issued to a very few countries and are for 15 days only. You would enter on a visa exemption of (currently) 45 days, pre-Covid 30 days.
Then you can extend the VE for another 30 days so your return ticket would need to accommodate this, if that is your plan.
The attached chart (with countries who need a Visa on Arrival highlighted) might make things clearer.