Can I submit a non-O retirement visa if it only allows single entry?

Immediately after you get your year extension inked in, then buy a multiple entry permit 3800 baht

If you want a multientry 1 year visa, apply for an OA.

The original non-O retirement is 90 days single entry. You need this time if you wish to extent for 12 months based on retirement as you need bank account etc. it is when you get the 12 month extension that you can choose single or multiple entry (if you are going to leave Thailand 3 times or more in that 12 months it’s worth getting the multiple)

You can only get single entry now

There is no multiple entry non-O visa. Most embassies haven't been issuing them for years, and the last ones that did stopped when they switched to e-visa in January.

The non-O gives you 90 days to arrive in Thailand, open your bank account, and get everything setup for your 1-year extension. You'll need to have your proof of funds in the account within 30 days because when you apply for your 1-year extension the money must have already been in your account for 2 full months.