you mean form 8615
Who Must File
Form 8615 must be filed for any child who meets all of the following
conditions.
1. The child had more than $2,200 of unearned income. capital gains are unearned income
2. The child is required to file a tax return. read the instructions (if your parents CAN'T claim you use Chart A, otherwise Chart B) https://www.irs.gov/pub/irs-pdf/i1040gi.pdf charts start on page 10
3. You were:
a doesn't apply since you say you were over 18
b. Was age 18 at the end of 2021 and didn’t have earned
income that was more than half of the child's support,
this would apply if you weren't 19 at the end of 2021
c. Was a full-time student at least age 19 and under age 24 at
the end of 2021 and didn’t have earned income that was more than
half of the child's support.
you don't meet this test because you were not a full-time student
4. At least one of the child's parents was alive at the end of
2021.
5. The child doesn’t file a joint return for 2021.
for 3 the actual code section is 1(g)(2)(A)(ii)
(I)has attained age 18 before the close of the taxable year and meets the age requirements of section 152(c)(3) (determined without regard to subparagraph (B) thereof), and
(II)whose earned income (as defined in section 911(d)(2)) for such taxable year does not exceed one-half of the amount of the individual’s support (within the meaning of section 152(c)(1)(D) after the application of section 152(f)(5) (without regard to subparagraph (A) thereof)) for such taxable year,
if you are subject to the kiddie tax, the alternative is for your parents to use form 8814 to report your income and pay your taxes form 8814
