Only certain Discord servers have the tag feature. I moderate/admin multiple servers and only one of them, which has no boosts mention the server tag option, which we can't use b/c it lacks boosts. Maybe the other Discord devs can pull their heads out of their asses to see which servers are actually popular rather than have the feature set exclusively to random servers. I don't believe there was a timeframes for how long it'll be before more servers get the server tag options. I don't believe there was a timeframes for how long it'll be before more servers get the server tag option. Here is what it would look like in server settings.
The profile section of user settings is where server tag options to choose from would be.