The short answer, then what it means for your logo and text.
Square or portrait?
Square posts (1:1) still work, but a 4:5 portrait is 25% taller at the same width, so it gets more of the screen as people scroll.
Making posts at the right size
In Cutlin, choose Portrait 4:5, tagged Instagram post, in Configuration and the picture comes back at exactly 1080 × 1350. Generate for social media remakes a picture at that size with important content inside the safe area, and Check for social media looks a finished post over before you publish it.
