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Try 1.16.5-36.1.25 and provide us with the logs from both sides. I added some extra logging to make it easier to figure out what packet is being bad.

Player in question here, here's the log: https://gist.github.com/Garyzan/c58f5e7da81989b77387c73f8117c048

this is the newest server log: https://gist.github.com/Bossos11/a327cf553b0642b2c095cc54f72c3c07 (the player will send the log himself)

the files of the server are created in the run folder of your forge mdk. As @vemerion has already explained you have to accept the eula, you also have to know that you are not logged into your IDE-Minecraft with a mojang account, which is why you have to set the option "online-mode" in the server server.properties file to false (Edit: this file is created at the second start after the eula has been accepted), otherwise you cannot join the server.

Ah yes. I wondered if this was the case. You're trying to change the weather using a GUI screen. https://github.com/NoEffort/NuggetMod/blob/main/src/main/java/me/noeffort/nuggetmod/client/screen/WeatherPedestalScreen.java#L82 That code cannot and will not ever work because only the client knows about it.

Things related to input and graphics are done on the client. Most other things related to the actual logic of the game should be done on the server. A bit of common sense goes a long way. For example, if you want to damage the player, you only want to do that on the server, since it is the server that keeps track of all the players and their state. If you want to place a block, you have to do it on the server, otherwise you end up with 'ghost-blocks' etc. When you use runServer for the first time a text file called eula.txt should be generated, which you have to edit to set 'eula=true' and then run the server again. But using runServer is not guaranteed to catch all errors related to sides, since it will only crash if you are using a method on the physical server that only exists on the physical client (for instance rendering methods). This page explains it in pretty good detail.

Player movement is controlled by the client, that is you need to set the movement on the client.