Sharepoint - If A = 2, then set B to yes

Your A column is choice field with Choices (1, 2, 3).

Your B column is Calculated field with type Yes/No.

For B column calculation formula is:

=IF(A="2",TRUE,FALSE)

Column A

FINAL

You are close, but you only need to enclose your values in quotes if you need the values evaluated as strings.
Assuming you configured column 'A' as a numeric field type, and you have configured 'B' as a Calculated column with a Boolean (yes/no) output, then the following should work:

=If([A]=2, TRUE, FALSE)