Templates (and editing them) has apparently been moved from Customize in the Project toolbar to the new Workflow button (screenshot attached). The Help Center page on Task Templates needs to be updated to reflect this.
Hi @Tristan_Schmid , welcome to the forum 
Thanks for raising this. Indeed the Customize button has been renamed to Workflow recently, with yet another redesign of the order of categories within. However, it appears to be an A/B test or a gradual roll out as it is not the case in all the spaces of clients we work with, yet.
Indeed the screenshots in the Help Center article are outdated - sometimes they lag behind but generally I’ve noticed the Help Center team are pretty good at keeping up with the countless updates we get every month! 
By the way, don’t forget to vote for yourself!
Piniging the @Forum-team to get this to the right team!
Hi @Tristan_Schmid, and welcome to the Forum!
Thank you for flagging this. The rollout of the new layout is not completed yet, which might be a reason behind the Help Center page not yet being updated, but I have given the right team a little nudge, just in case!