The Undertaker is now planned to be a part of WWE's return to the Kingdom of Saudi Arabia on Friday, May 3, according to the Wrestling Observer Newsletter. The booking was reportedly confirmed this past week.
There were at least some issues between Taker and WWE due to the Starrcast II convention booking Taker accepted for May, during AEW's Double Or Nothing weekend in Las Vegas. The Observer notes that whether or not those issues were settled, they weren't strong enough to keep Taker off the Saudi show, which would be a big payday.
It's possible that Taker's return to the WWE ring won't come until the show in Saudi Arabia as there's still no word on The Dead Man working WrestleMania 35 next month.
Update: The Undertaker and Michelle McCool visited the WWE Performance Center in Orlando earlier this week, according to PWInsider.