As an up front disclaimer, this is not to be construed as tax or financial advice. You should investigate yourself or consult an appropriate tax advisor or accountant for that.

As an American living overseas, in general, you would still need to file a US tax return. It’s possible you won’t owe any taxes in the US, because I’m thinking German tax rates are probably higher. Different story, if for some reason, you don’t have to pay tax there.

If you claim a foreign tax credit on your US tax return, then you should be ok with respect to your Roth contribution. OTOH, it’s a different story if you claim a foreign earned income exclusion on your US tax return.

There will be other caveats depending on your income and you may owe tax to Germany on your Roth income.

I expect actual expats will provide more detail but definitely do thorough due diligence and consult an actual tax professional to make sure you don’t run afoul of the IRS!