You likely didn't receive a 1040 SE form because you didn't have self-employment income of $400 or more. This form is used if you have earned income from self-employment work and need to pay self-employment taxes like Social Security and Medicare.
As a trader, your trading gains are generally considered capital gains, which are not subject to self-employment tax. Therefore, you wouldn't need to file a 1040 SE form for Social Security purposes
