What are the most effective exercises for building core strength at home?

Stop masturbation ☁️

Leg raises Sit ups Plank

I follow this routine as a beginner. Feels good to keep my self injury free. https://youtube.com/playlist?list=PL9jpSjr09H4fGAIbeU1obS0dI_Ugdpts2&si=gXFBsh7dU0ZYZvrE

Planks mostly , search on youtube tho

Probably. Sitting on a chair.