customer claims they do scrum but they have quarterly planning events (2 full days) where we need to estimate and plan everything for the next 3 months.

Manager: "last quarter I calculated your velicoty so now you get 4 story points per sprint per developer"
Team: "But you started us off at just 5 per sprint that's too small"
Manager: "Ok but if you only did 4 why do you now want 20"
Team: "Because it's arbitrary and we say we want to"
Manager: "1 story point is 1 day"
Team: "story points aren't time"
Manager: "4 story points is 1 sprint"
Team: "but a sprint is 10 days"
Manager: "the junior dev can do 4 story points per sprint and the senior dev can do 4 story points per sprint"
Team: ...