No date announced yet. The new PV is here. This announcement comes after the final episode of season 3 aired earlier today. Check out the ANN article for additional information. Synopsis of the source novels from AniList:
Living alone and never having had a girlfriend, 37-year-old Satoru Mikami is dissatisfied with how his life has turned out. But after dying at the hands of a robber, he awakens to a fresh start in a new world…as a slime monster.
I always figured slime is a story about the power of friendship, so sometimes you need some chatting around a table because friends don’t just use demon lord powers on each other all the time.