why?

It's supposed to replace the Player Reporting button rather than the Options one… Which version are you on and what mods do you have?

In general it's MC 1.21, Fabric API 0.102.0, Fabric Loader 0.16.0 and Custom Lan 2.3.1, as for the other mods I added an excerpt from the logs which hopefully provides enough information
mods_from_logs.txt

Ah, it's because you've set “Game Menu” in Mod Menu's options to “Insert”. As a workaround for now, you can set it to “Replace”.

However I need to find a more reliable way to find the Open to LAN button, because there's issues with other mods as well, such as #38…

Alright, I made it find it by text rather than index, which should be more reliable and fix this.