SummerSMP 1.21.1 has just opened with Season One, and it is built for players who want a familiar SMP feel with a harder edge. If you like survival, looting, and a bit of pressure from PvP, this place is set up for that. It is also crossplay, so more players can jump in and play together.
There is no claiming system here, so base building and survival actually matter. The server includes an Auction House, ordering system, bounty system, duels, and sell multipliers to keep the economy moving while still keeping the PvP side active. It also uses a fast crystal PvP setup for players who enjoy that style.
The world borders are set out pretty clearly too: Overworld 15k x 15k, Nether 10k x 10k, and End 10k x 10k. If you want a challenging survival SMP with PvP, economy features, and no claim protection slowing things down, SummerSMP is worth checking out.