He died in May of 2021. I think it was some kind of heart issue. However, he has basically a close friend he talked to about for his plans and the ending of the manga as well as concept designs and such he left behind. Obviously there was a pause in releases when he died, but I think after some time and his family talking with the friend they agreed to let the friend continue the manga as the original author planned. Below is about the announcement I gabbed from wiki
“On June 7, 2022, Hakusensha and Kouji Mori announced that Berserk would continue publication, using plans and thoughts that were relayed to Mori by Miura himself, as well as memorandums and character designs that Miura left behind.[40] As the only person who knows the ending Miura intended, Mori agreed to continue the series and promised "I will only write the episodes that Miura talked to me about. I will not flesh it out. I will not write episodes that I don't remember clearly. I will only write the lines and stories that Miura described to me."
How has it been a decade and it still hasn’t finished