22 And therefore it was imputed to him for righteousness.
Look closely at the verses you included.
Abraham "staggered not at the promise of God through unbelief but was strong in faith". The reason Abraham's belief gave
glory to God was only because it was God who imputed to Abraham that faith - V20.
Because of Christ's faith imputed to Abraham, Abraham became persuaded (V21).
It doesn't say righteousness was imputed to Abraham because of Abraham's faith; it says that faith was imputed to Abraham to give him (for) righteousness (V22). Please focus in on and understand the difference between the two.
The "it" of the verse, is faith that had been IMPUTED to him for righteousness -- it was not Abraham's faith - it was Christ's faith that was "IMPUTED TO HIM" - that's the only way righteousness is/can be obtained.
Abraham's faith, were it possible to actually be of/from Abraham, would have of itself no righteousness because he, like us all, have no righteousness. Instead, the righteousness of the verse could only have been through Christ's righteousness. See the below verses.
In 4:9, do you see that "faith was reckoned to Abraham for righteousness" (bolded, underscored)
[Rom 4:9 KJV] 9 [Cometh] this blessedness then upon the circumcision [only], or upon the uncircumcision also? for we say that faith was reckoned to Abraham for righteousness.
In 3:9 do you see that righteousness is only through the faith of Christ (bolded, underscored).
[Phl 3:9 KJV] 9 And be found in him, not having mine own righteousness
, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith: