I recommend the math discord in addition to mathoverflow and mathstodon. https://discord.gg/math https://discord.gg/math I got help with grad-level problems th

I recommend the math discord in addition to mathoverflow and mathstodon. https://discord.gg/math https://discord.gg/math I got help with grad-level problems there. There's discussion there from high school through research, and is quite active.