can i file my taxes for 2021 for the stimulus?

If you could be claimed as someone else's dependent for 2021 you are not eligible for the recovery rebate credit.   If you did not receive the 3rd stimulus and you were eligible, fill a 2021 return by April 15, 2025 or it will be too late.

You should check your online account with the IRS---many people received the 3rd stimulus before they filed their 2021 return, so they did not need to use the credit on their tax return.

Look at your online account with the IRS to see if they sent you $1400 in 2021.

https://www.irs.gov/payments/your-online-account

2021

https://www.irs.gov/pub/irs-pdf/i1040gi.pdf

Here is the IRS 2021 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2021.pdf

or if you want bigger type use 1040SR for Seniors,
https://www.irs.gov/pub/irs-prior/f1040s--2021.pdf

And 2021 Instructions
https://www.irs.gov/pub/irs-prior/i1040gi--2021.pdf

2021 Tax and EIC Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2021.pdf

Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2021.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2021.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2021.pdf