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

Stop masturbation ☁️

I follow this routine as a beginner. Feels good to keep my self injury free.

https://youtube.com/playlist?list=PL9jpSjr09H4fGAIbeU1obS0dI_Ugdpts2&si=gXFBsh7dU0ZYZvrE

Leg raises
Sit ups Plank

Probably. Sitting on a chair.

Planks mostly , search on youtube tho