Have you ever come across the issue: When you’re doing the Rotate command and have specified the base point and 90 degrees, but it is not actually 90 degrees to the point you’ve chosen?

Just check your Drawing Units settings, you won’t get 90 degrees rotation if you have accidentally selected “Grads” , as shown in the following picture,

Enter UNITS and press Enter key to open the Drawing Units dialog box,

The solution to the problem is to set it to Decimal Degrees or Deg/Min/Sec, shown as below,

After the setting, you should have an object rotated 90 degrees.