I received an email from JLCPCB, however I am not seeing how it could be a substitute:
Hi sir ,
Thanks for your email, my colleagues applied to purchase it for several times recently , but been rejected by purcahsing department because of high cost and supply resource shortage , so we do not know when will it be restocked , very sorry .
I tried to find another item C14909 which has the similar description with ATTINY841-SSU, please take some time to check it , thanks !
Wish you all the best
Ryan