Do I claim my wife as a dependant in order to get a standard deduction for her on a married joint return?

No.  A spouse is never a dependent.  What Standard Deduction amount did you get?  It's either for Single or Married not the number of people.  Check 1040 line 12.

For 2020 the standard deduction amounts are:

Single 12,400 + 1,650 for 65 and over or blind (14,050)

HOH 18,650 + 1,650 for 65 and over or blind

Joint 24,800 + 1,300 for each 65 and over or blind

Married filing Separate 12,400 + 1,300 for 65 and over or blind

Personal exemptions were removed from the tax code after tax year 2017.

A spouse can Never be claimed as a dependent.  You should be filing as Married Filing Jointly even if one spouse has little or no income.  You receive the highest Standard Deduction for MFJ.

Standard deductions for 2020

Married Filing Jointly - $24,800 add $1,300 for each spouse age 65 or older