UPDATE: Using Craftbukkit instead of ther normal server-client fixed my issue completely, thanks so much to TileEntity for helping me out!
-I've tried looking through every forum, youtube tutorial, and article I could find about fixing this issue and I can't seem to find a way to fix this. So I'm trying to make a Minecraft server for me and my girlfriend to play on, and I don't want to just pay a website for hosting. I'm trying to run a 1.16.2 server.
Ok I tried Spigot and nothing changed, but when trying Craftbukkit, the Minecraft server status showed that it was able to get a Cached Result, while originally it wasn't able to. I can't test this with another player right now, as it's 4 AM here atm, but I'll update the post if it works. Thanks much! This is already a lot of progress compared to everything else I've done.
Edit: UPDATE, using Craftbukkit fixed the issue completely. Thanks so much! you're a lifesaver