I found a hardcore survival SMP called LUMI HARDCORE and it is mostly vanilla with one big rule. You only get one life.
If you die you do not come back right away. You end up in an infirmary until the next reset and there are no revives.
The world resets every 60 days so each season uses a brand new seed. That means nobody keeps a huge head start for long and everyone gets a fresh start together.
It is whitelisted so you have to apply to get in. It also supports both Java and Bedrock since crossplay is enabled.
