This question is specific for Zoom calls...assuming you use video on calls.
Two category buckets: Internal and External
Internal calls - I can justify more casual dress; t-shirt/sweatshirt...unless it's with my boss or leadership and then I'll put on a polo.
External calls - Always either putting on company branded apparel or a polo/button shirt.
And I always avoid a hat...it at least gives the appearance that I put some kind of effort to look presentable, even if I'm in a t-shirt on a team call.
Sidenote: I use a halo-style light for my video calls. It really helps improve the overall quality, regardless of how well lit your space is already.
BONUS QUESTION: What do you wear for a video interview?