Clicking the link on the browser which adds an external server will take you the Friends tab instead.

How to reproduce:

Type the following URL:

minecraft://?addExternalServer=(ServerName)%7C(URL of the server:(Port))

(also make sure that minecraft is running in background)

for example:

minecraft://?addExternalServer=SkyBlockPE%7CPlay.SkyBlockpe.com:19132

Results:

Takes you to the Friends Tab. ->

Maybe the reason for this is because External Servers would be put in the Friends Tab before Featured Servers were a thing.