Resources suitable for A level and IBDP:
3Blue1Brown videos
AMSP A level videos
AMSP Further Maths videos
ATM Proof booklet
BossMaths Sixth Form
Desmos resources
DrFrostMaths KS5
Geogebra resources
Imperial College A level
Interactive Maths IB skills
James Tanton GMP
Jethwa Maths
Jo Morgan Resourceaholic
Khan Academy