Do I need a special visa to rent a condo in Bangkok and travel between the US and Thailand?

You’re better off with a retirement visa for coming and going the whole year. Immigration will frown on you coming back every other month on a visa exempt or a tourist visa.

I work in Oz for 4 weeks and go to Thailand visa exempt for 2 weeks and have never had any issues with immigration.

Condos don't care about Visa. You probably can do Visa Exempt a couple of times. Then I'd suggest getting a multi-entry e-visa (tourist visa). I was doing similar for a couple of years. No problems. Now have DTV for longer stays. I think the trick was going back to the USA, versus a neighboring country. And staying in the USA a couple of months before returning to Thailand.

They will take your money amd 2 month deposit. However, your visa situation might be another issue

I don’t see the visa (or exemption) working that well if you are a frequent visitor.

Perhaps look at a ling term visa. DTV, LTR, Elite, or non O if you are over fifty.

You can probably rent a condo with any type of visa, even visa exempt. However, even if you treat it like a holiday place and just spend time in Thailand a while and back in the states a while, there is always a possibility of being denied entry unless you have a proper long term visa that allows you to enter and exit at will. And the consequence of being denied entry is that the place you have rented and probably left your things will just be taken back by the owner and rented out again. And if you are lucky, they will not ask for remaining rental as per contract.

You don’t need a visa to rent a condo, just funds.

renting a condo apartment doesn't cut any ice visa-wise. In case you are not yet 50 years old (so unable to secure a 1-year "retirement extension" or a LTR visa) your visa options are limited. You culd try to get the DTV visa, with which you will get stamped in for 180 days upon each entry, that within a visa validity period of 5 years

I'm what I gathered, after 6 MO this you will be at the mercy of the immigration officer.

I wouldn't do it with this setup. Try Philippines, Cambodia or Vietnam.

Visas and rental contracts are completely separate. You can rent a condo on any visa type (or exempt entry).