So I tested that Geyser MC thing and it works! I was able to join my test Java server from my bedrock Windows client and interact with the Java client.
Part of me wants to buy Minecraft on mobile ($6.99) just to test that as well. The only caveat is Geyser (and any other third party server for that matter) work with Switch or console players without them configuring their networks differently, as per [https://apexminecrafthosting.com/how-to-join-a-bedrock-edition-server-on-xbox-switch/].