Just wanted to point out that there's a pretty interesting project called Geyser[0] (along with a plugin called Floodgate[1]) that allows Java and Bedrock Minecraft users to connect to the same Java server. This might be an avenue the author could take to allow the tailscale auth here to work. In my implementation I'm using PaperMC[2] as well.

[0] https://github.com/GeyserMC/Geyser

[1] https://github.com/GeyserMC/Floodgate

[2] https://papermc.io/