Your rolled over 401ks now residing in an IRA are subject to the pro rata rule. There is an easy fix if your current 401k allows. Look for an option to roll your current IRA into your 401k. That will then allow you to do a regular backdoor roth. If your 401k allows you to roll in your IRA, then it may also allow you to do a mega backdoor roth. That isn't offered by every company, but you want to look in the 401k plan documents for an option to do after tax contributions and a Roth conversion or in service withdrawals of after tax contributions.
The regular backdoor roth would work like this: Contribute up to your annual limit to an IRA, post tax so nothing new taxwise, then convert that contribution to a Roth IRA. It takes a few days for the contribution to clear so if you hold it in a money market account you'll earn a few bucks of interest. Roll everything into the Roth. You'll get a 1099 at the end of the year for just the interest portion. Ex. Contribute $5k to IRA. Earn $4 interest before the conversion. Convert $5,004 to Roth and your 2024 1099 will be for $4.
You should also note that there are 2 separate 5-year rules for Roth accounts. The first is generally that you have to have the money in the Roth account for 5 years before you can withdraw the gain tax free, contributions can be withdrawn. This no longer applies when you turn 59 1/2 even if you have not held the account for 5 years. The second is that in order to take advantage of the tax free aspect of a Roth account, you need to have contributed to a Roth account more than 5 years ago. This does not go away when you turn 59 1/2. You can have multiple Roth accounts with multiple brokerage houses, so long as you contributed to one of them 5+ years ago the rule is satisfied for all of your Roth accounts. For flexibility's sake, it's a good idea to set up a Roth IRA and fund it with at least a couple bucks even if you aren't going to regularly fund it just to get that second 5-year rule out of the way.
*edit-On the 5 year rules, for both it's 5 tax years. Even if you contribute on December 31st, that gets counted as a full tax year, so it could really be just over 4 calendar years. The First 5 year rule that is only for conversions but again it goes away if you are over 59 1/2.