FYI you can do backdoor Roth contributions even if you already have an IRA with funds in it. It's just more complicated because you have to follow the pro rata rule.
The PITA of that is that you have to keep track of the post tax additions pretty much for ever afterward or you’ll end up paying double tax on them.
And if you have hundreds of thousands or millions in the traditional. The pro rata rule would make your backdoor contribution 90+% taxed so it would be pointless