Cannot enter multiplayer mode

I recently bought Minecraft Java edition using my Microsoft account (i.e. I don't have a Mojang account) and I try to use multiplayer. When launched, only the singleplayer option is available and the multiplayer option is grayed-out, with hover text: "Multiplayer is disabled. Please check your Microsoft account settings".

I don't have any such setting in my profile at minecraft.net, xbox.com or microsoft.com... I browse in cycles through those different websites, which just refer me from on to the other...