[10:20:58] [main/INFO]: Loading for game Minecraft 1.16.5
[10:20:59] [main/FATAL]: A critical error occurred
net.fabricmc.loader.discovery.ModResolutionException: Could not find required mod: byg requires {fabric @ [*]}
at net.fabricmc.loader.discovery.ModResolver.findCompatibleSet(ModResolver.java:180) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.discovery.ModResolver.resolve(ModResolver.java:787) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.FabricLoader.setup(FabricLoader.java:211) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.FabricLoader.load(FabricLoader.java:201) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:126) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotServer.main(KnotServer.java:28) [fabric-server-launch.jar:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_282]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_282]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_282]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_282]
at net.fabricmc.loader.launch.server.FabricServerLauncher.launch(FabricServerLauncher.java:62) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.setup(FabricServerLauncher.java:106) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:50) [fabric-server-launch.jar:?]
Caused by: net.fabricmc.loader.util.sat4j.specs.ContradictionException: Creating Empty clause ?
at net.fabricmc.loader.util.sat4j.minisat.constraints.cnf.Clauses.propagationCheck(Clauses.java:117) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.util.sat4j.minisat.constraints.cnf.Clauses.sanityCheck(Clauses.java:97) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.util.sat4j.minisat.constraints.MixedDataStructureDanielWL.createClause(MixedDataStructureDanielWL.java:81) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.util.sat4j.minisat.core.Solver.addClause(Solver.java:401) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.discovery.ModResolver.findCompatibleSet(ModResolver.java:177) [fabric-server-launch.jar:?]
... 12 more
container@pterodactyl Server marked as offline...

[Pterodactyl Daemon]: ---------- Detected server process in a crashed state! ----------
[Pterodactyl Daemon]: Exit code: 1
[Pterodactyl Daemon]: Out of memory: false
[Pterodactyl Daemon]: Aborting automatic restart, last crash occurred less than 60 seconds ago.

you need to install Fabric API for Biomes You'll Go.

You can download it from here: https://www.curseforge.com/minecraft/mc-mods/fabric-api/files. :)