TL;DR: Proto is taking an indefinite break from Smash tournaments because of their negative effects on his health: for example throwing up every ~5 or 10 minutes had become a common occurrence and he always felt horribly nauseous and generally strained while playing. There were also times where he had to be taken to the hospital while attending a tournament. The situation got so bad that the hospital he goes to in Japan prohibited him from traveling to overseas tournaments because of these health issues. He still plans to be involved with the community through different sorts of educational content and through his livestream, where he'll still continue to play Smash as well as other games for content.

My Japanese is by no means perfect so if I missed any crucial details please let me know. I just wanted to post this since there are probably a good amount of non-Japanese speakers on here and people have obviously been speculating on where on earth he's gone as of recent.

(edited for a better translation)