Togashi been updating on Twitter for a month now.
Chapters 401 to 410 are all done in some form or fashion. As of yesterday, 405 was done with dialogue and starting backround drawings. 410 was done with the inking. Kinda surprised he stuck with a 20 page format, would've thought that without having to publish on Shonen Jump, he would feel more liberty to do more (or less) depending on the chapter.
Also said he was starting work with 411.
It's interesting there's been no news about where it will be published, at this point it seems Jump+ is the only place. I'd expect an announcement in the July or August, probably a September return? If he decides to publish monthly he could have an entire year already done by that point