Presently there is the start of untested builds for 1.17 in the git, but the builds are not compatible. I've tested it and get the following error:
Tested Versions:
Paper Spigot 1.17.1 (in house modified build of 1.17.1-R0.1-SNAPSHOT)
MCCosmetics Version(s): 3.0 and 4.0
MythicMobs Version(s): 4.13.1/5.0.2/5.0.3
ModelEngine Version(s): r2.2.0/R2.5.1
The Error Dump
[23:03:58] [Server thread/INFO]: [MCCosmetics] Enabling MCCosmetics v0.3.0-dd6a975d
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loading MCCosmetics for Paper (MC: 1.17.1)...[0m
[23:03:58] [Server thread/INFO]: [MCCosmetics] The server is running PaperSpigot; enabled PaperSpigot exclusive functionality[0m
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loading Configuration...
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loading Configuration...
[23:03:58] [Server thread/INFO]: [MCCosmetics] MCCosmetics configuration file loaded successfully.[0m
[23:03:58] [Server thread/INFO]: [MCCosmetics] MythicMobs found; enabling MythicMobs support.
[23:03:58] [Server thread/INFO]: [MCCosmetics] PlaceholderAPI found; enabling PlaceholderAPI support.
[23:03:58] [Server thread/INFO]: [PlaceholderAPI] Successfully registered expansion: mcc
[23:03:58] [Server thread/INFO]: [MCCosmetics] Found custom selection menu for hats
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded 6 hats.
[23:03:58] [Server thread/INFO]: [MCCosmetics] Found custom selection menu for backs
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded 6 backs.
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image hearts
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image sus
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image flamental
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image skull
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image gg
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image laugh
[23:03:58] [Server thread/INFO]: [MCCosmetics] Loaded image flame
[23:03:59] [Server thread/INFO]: [MCCosmetics] Loaded 7 spray images
[23:03:59] [Server thread/INFO]: [MCCosmetics] Found custom selection menu for sprays
[23:03:59] [Server thread/INFO]: [MCCosmetics] Loaded 7 sprays.
[23:03:59] [Server thread/INFO]: [MCCosmetics] Found custom selection menu for offhands
[23:03:59] [Server thread/INFO]: [MCCosmetics] Loaded 2 offhands.
[23:03:59] [Server thread/ERROR]: Error occurred while enabling MCCosmetics v0.3.0-dd6a975d (Is it up to date?)
java.lang.NoClassDefFoundError: com/ticxo/modelengine/api/model/base/BaseEntity
at io.lumine.cosmetics.MCCosmeticsPlugin.enable(MCCosmeticsPlugin.java:109) ~[MCCosmetics.jar:?]
at io.lumine.cosmetics.utils.plugin.LuminePlugin.onEnable(LuminePlugin.java:73) ~[MCCosmetics.jar:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[server.jar:git-Paper-"cc43ba7"]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:370) ~[server.jar:git-Paper-"cc43ba7"]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:500) ~[server.jar:git-Paper-"cc43ba7"]
at org.bukkit.craftbukkit.v1_17_R1.CraftServer.enablePlugin(CraftServer.java:561) ~[server.jar:git-Paper-"cc43ba7"]
at org.bukkit.craftbukkit.v1_17_R1.CraftServer.enablePlugins(CraftServer.java:475) ~[server.jar:git-Paper-"cc43ba7"]
at net.minecraft.server.MinecraftServer.loadWorld(MinecraftServer.java:733) ~[server.jar:git-Paper-"cc43ba7"]
at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:317) ~[server.jar:git-Paper-"cc43ba7"]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1220) ~[server.jar:git-Paper-"cc43ba7"]
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:319) ~[server.jar:git-Paper-"cc43ba7"]
at java.lang.Thread.run(Thread.java:831) ~[?:?]
Caused by: java.lang.ClassNotFoundException: com.ticxo.modelengine.api.model.base.BaseEntity
at org.bukkit.plugin.java.PluginClassLoader.loadClass0(PluginClassLoader.java:151) ~[server.jar:git-Paper-"cc43ba7"]
at org.bukkit.plugin.java.PluginClassLoader.loadClass(PluginClassLoader.java:103) ~[server.jar:git-Paper-"cc43ba7"]
at java.lang.ClassLoader.loadClass(ClassLoader.java:519) ~[?:?]
... 12 more
[23:03:59] [Server thread/INFO]: [MCCosmetics] Disabling MCCosmetics v0.3.0-dd6a975d
[23:03:59] [Server thread/INFO]: [MCCosmetics] Disabling MCCosmetics...[0m
[23:03:59] [Server thread/WARN]: java.lang.NullPointerException: Cannot invoke "io.lumine.cosmetics.players.ProfileManager.unload()" because "this.profiles" is null
[23:03:59] [Server thread/WARN]: at MCCosmetics.jar//io.lumine.cosmetics.MCCosmeticsPlugin.disable(MCCosmeticsPlugin.java:151)
[23:03:59] [Server thread/WARN]: at MCCosmetics.jar//io.lumine.cosmetics.utils.plugin.LuminePlugin.onDisable(LuminePlugin.java:79)
[23:03:59] [Server thread/WARN]: at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:266)
[23:03:59] [Server thread/WARN]: at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin(JavaPluginLoader.java:399)
[23:03:59] [Server thread/WARN]: at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManager.java:537)
[23:03:59] [Server thread/WARN]: at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:374)
[23:03:59] [Server thread/WARN]: at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:500)
[23:03:59] [Server thread/WARN]: at org.bukkit.craftbukkit.v1_17_R1.CraftServer.enablePlugin(CraftServer.java:561)
[23:03:59] [Server thread/WARN]: at org.bukkit.craftbukkit.v1_17_R1.CraftServer.enablePlugins(CraftServer.java:475)
[23:03:59] [Server thread/WARN]: at net.minecraft.server.MinecraftServer.loadWorld(MinecraftServer.java:733)
[23:03:59] [Server thread/WARN]: at net.minecraft.server.dedicated.DedicatedServer.init(DedicatedServer.java:317)
[23:03:59] [Server thread/WARN]: at net.minecraft.server.MinecraftServer.x(MinecraftServer.java:1220)
[23:03:59] [Server thread/WARN]: at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:319)
[23:03:59] [Server thread/WARN]: at java.base/java.lang.Thread.run(Thread.java:831)
