@Heras,
This can be set on your Youtube channel – simply go to YouTube studio, then Customization settings. From there, you should be able to add text/your referral link on the banner.
Thanks Mattches for the insight! If you want me to flag your post as “solution”, just copy the step by step solution in it (and if my guesses about english names for the section are wrong, you can correct it).
Step by step solution :
Go to the main page of your channel
Click on “Personnalize channel” (or something like that, My YT is in French)
Go to “General informations”
Add the links you want on your banner. You can put Facebook, Brave, uTip, Tipeee, Spreadshirt or whatever you want. Maximum 5 links will be displayed, but you can limit the number of links if you want.