Followed the steps to install SpongeForge. Did the latest from a couple days ago, 52.0.3-12.0.0 and downloaded the same version of Forge (52.0.3).
Server starts fine without SpongeForge and I have no plugins or mods installed.
Here is "debug.log"
[09Jan2025 11:00:48.433] [main/DEBUG] [mixin/]: mixins.sponge.api.json:itemstacklike.item.inventory.transaction.SlotTransactionMixin_ItemStackLike: Class version 65 required is higher than the class version supported by the current version of Mixin (JAVA_18 supports class version 62)
Whats your java version?
I just updated to 21.
As in that log was created when you had java 21?
Yes. I updated to 21 shortly after my first attempt at starting the forge server, before putting SpongeForge into the mods folder
Sorry fell asleep. What was your previous java?
It was java 17.