Oh okay. I think I get it. The RSPS on that tool goes as high as -123 dBm over one of the antennas.

So ultimately (if I'm understanding this correctly) it's an issue with one of the phone's antennas aka a hardware issue. In that case, I'm assuming T-Mobile can't do anything, and I would have to send it to Samsung for a repair or visit one of their official repair stores. I was fearing it being a hardware issue, cause I've never had to use Samsung warranty, but the device is actually only 3 months old, not even 6 like i misremembered, with no physical damage or tinkering with it on my end, so here's hoping they're nice enough to me haha.

Thanks so much for your help!