Bad cell signal on Flip 4 using Mint/TMobile?

Hey all, I recently bought an unlocked Z Flip 4 and have been having some network issues. I was hoping to get insights on if this is a problem with the phone (most sites say it has great service), or just this phone.

I have Mint Mobile, which is on TMobile, and have had pretty bad signal, especially when I am inside. I'll get that circle with an X, and can't even send a text. Sometimes I'll have a couple bars, but when I go to send a text the bars will disappear.

Previously I had a OnePlus 7 pro and would have no issues with cell signal.

If it matters, I was having issues with the 5g, and had to just make the phone use LTE/3G/2G.

Any help would be appreciated. I'm really liking this phone, but losing signal inside, and in some of my other regular spots is a dealbreaker.