The OP has money that he rolled into a traditional IRA from a 401k and he is asking about doing a backdoor Roth.

There is no advantage and it isn’t a strategy to put it in a 401k first.

A Roth IRA is desirable to have money in because all of the growth is not taxable when it is eventually pulled out in retirement.

The OP would be able to contribute straight to a Roth IRA if they have income under $230k (married).

If income is higher than $230k, what you do is you contribute to a traditional IRA. The contribution is after tax because you are above the income limit. Then you convert that to a Roth. That is what is called a backdoor Roth IRA.

The catch is you can’t have other money sitting in any IRA besides your Roth or you run into tax issues on the conversion.