I got an answer from Aimchess via Facebook Messenger yet
Me:
The site and app is down since a few days. I'm a fan and subscriber. When will it be back again? I need some lessons 😉
Aimchess:
Hey Markus! Thanks for reaching out, we're aware of the issues with the site, we're working on a fix at the moment, we're hoping to be online as soon as possible and will be issuing a statement later today!
Because Aimchess seems to be owned by PLAY MAGNUS https://playmagnusgroup.com/brands/aimchess/ i asked them via email at ir@playmagnus.com on June 15th about Aimchess but got no answer until today.
Maybe Magnus https://www.chess.com/member/magnuscarlsen as a major shareholder of Play Magnus knows more?