In the "summary" section of TurboTax, there is a line marked "other taxes"? Please explain what that might be?

The "Other taxes" line includes a range of taxes other than income tax, all which are collected via Form 1040. These include:

• Self-employment tax from Schedule SE,
• Unreported Social Security and Medicare tax,
• Additional tax on IRAs, other qualified retirement plans, and other tax-favored accounts,
• Household employment taxes from Schedule H, and
• Health care: Individual responsibility payments.

These taxes are summarized on Schedule 4 (Form 1040).

I withdrew my RMD and I understand this was not taxable in 2020 so why is there a tax charged in "other taxes" when I rolled over my RMD back into the same IRA?

The rollover transaction isn't taxable unless the rollover is to a Roth IRA or a designated Roth account, but it is reportable on your federal tax return. You must include the taxable amount of a distribution that you don't roll over in income in the year of the distribution.

@rbritt2657

Other tax 

It could be many things.  Typically:  Self-Employment Tax, NIIT tax, AMT Tax, Penalties for early withdrawal from an IRA, etc.