mine says

[19:46:19 ERROR]: Could not load 'plugins/lifesteal-smp-plugin-1.6.4.0.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: Unsupported API version 1.17
at org.bukkit.craftbukkit.v1_16_R3.util.CraftMagicNumbers.checkSupported(CraftMagicNumbers.java:361) ~[patched_1.16.5.jar:git-Paper-771]
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:149) ~[patched_1.16.5.jar:git-Paper-771]
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:414) ~[patched_1.16.5.jar:git-Paper-771]
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:322) ~[patched_1.16.5.jar:git-Paper-771]
at org.bukkit.craftbukkit.v1_16_R3.CraftServer.loadPlugins(CraftServer.java:393) ~[patched_1.16.5.jar:git-Paper-771]
at net.minecraft.server.v1_16_R3.DedicatedServer.init(DedicatedServer.java:269) ~[patched_1.16.5.jar:git-Paper-771]
at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:1069) ~[patched_1.16.5.jar:git-Paper-771]
at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:291) ~[patched_1.16.5.jar:git-Paper-771]
at java.lang.Thread.run(Thread.java:829) [?:?]

You are loading in a version that is not 1.17, use 1.17