as i just noted in this topic…
https://eu.forums.blizzard.com/en/wow/t/time-to-remove-the-services-channel-and-ban-boosters/500947/133
it is only the “trade services” channel which is now set to auto re-enable itself across all chat tabs, and to stop it from happening, instead of simply unchecking the channel for each tab, you have to fully unsubscribe from that channel by clicking the red button on the right hand side, in the channels section of the chat settings.
Right click a chat tab, go to Channels, find the Trade (Services) channel and hit the red Ghostbusters icon on the right next to it.