Calculating capital gains on sale of overseas real estate ?

Apologies, as this question has likely been asked before though after searching/skimming this subreddit for twenty mins I'm still confused.

I'm a NPR in Japan 10+ years on a spousal visa. I've been earning some income in both Japan and the US, filing taxes for both with Japan as my tax home. Due to unforeseen events, I may be forced to sell a rental property I own in the US.

There will be capital gains tax on the sale of the property (i.e., on the amount that is the difference between the sale price and the fair market value of the property when I acquired it), though I'm unclear on the details.

Question: how do I determine the tax rate? E.g., if I have $50k in income and sell the house for $750k in 2026, do I include the $750k in my annual income for calculating the tax rate for capital gains?

I assume that I pay capital gains to the Japanese NTA, and then report this to the IRS so I won't have to pay the tax twice.

Any advice on this would be very helpful, thanks.