If im receiving ssi an someone claim me as a dependent last year but not this year can i still file this year to receive the recovery rebate

[DMarkM1]

If you cannot be claimed on someone else's 2020 tax return you can file a 2020 tax return and claim a Recovery Rebate Credit. Even if you are not claimed as dependent, the question you are asked is "Can you be claimed...?"

If you were not a full-time student and made over $4300, not including SSI, for the year in 2020 then you most likely cannot be claimed as a dependent. If you provided over 1/2 your own support your would not be a dependent either (SSI is someone else providing support not you).  Below are the criteria for qualifying as a dependent.  

Qualifying Child: 

1. The child must be your son, daughter, stepchild, foster child, brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant of any of them.

2. The child must be (a) under age 19 at the end of the year and younger than you (or your spouse if filing jointly), (b) under age 24 at the end of the year, a student, and younger than you (or your spouse if filing jointly), or (c) any age if permanently and totally disabled.

3. The child must have lived with you for more than half of the year.

4. The child must not have provided more than half of his or her own support for the year.

5. The child must not be filing a joint return for the year (unless that joint return is filed only to claim a refund of withheld income tax or estimated tax paid).

Qualifying Relative:

1. The person can't be your qualifying child or the qualifying child of any other taxpayer.

2. The person either (a) must be related to you in one of the ways listed under Relatives who don't have to live with you , or (b) must live with you all year as a member of your household (and your relationship must not violate local law).

3. The person's gross income for the year must be less than $4,300.

4. You must provide more than half of the person's total support for the year.

[Hal_Al]

Under the CARES Act, if you are claimed, or qualify to be claimed, as a dependent on someone else’s 2019 return you cannot receive a stimulus check, in 2020.   If you qualified as a dependent for 2019, but will not be for 2020, you will most likely get it in 2021, when you file a 2020 tax return.

Note that the requirement is not just whether you are actually claimed as a dependent, it's whether you qualify to be claimed as a dependent. 

So, the issue is: what changed in 2020 that you no longer qualify as someone's dependent.