How many times can you extend a 90-day non-immigrant O visa, and what is the difference between an O and OA visa?

I was here on an OA for 6 years. For both the O and the OA you typically eventually end up getting 1 year extensions. While getting 1 year extensions the only difference between an O and OA is the required health insurance for the OA. There was no insurance requirement when I got my OA in 2017 so now I would recommend the O as a better choice. With an O visa you have more flexibility about insurance choices if you choose to have insurance.

Now I am on the 10 year pension LTR visa. That also has an insurance requirement though that particular requirement is a little more flexible. The LTR has some steep financial requirements. It is worth looking into as a possible option.

Renew indefinitely if your circumstances don't change.

OA is an option for multiple one year entries if you have insurance coverage until the expiration date which is a year after approval date.

O visa is generally 90 days single entry.

You cannot renew any visa, there is no such thing as a visa renewal.

There's also no such thing as a 1-year non-O based on retirement.

There's a 90 day non-O visa for retirement, and based on that you can apply for a 1 year EXTENSION if you qualify. You can do this every year forever, as long as you continue to qualify. Each extension is a brand new application, not a renewal.