T-Mobile supports these bands:

• 5G: n2/41/71/258/260/261
• 5G,ER: n25
• 4GLTE: B4/5/12/71
• 4GLTE,ER: B25/66
• 2G,GSM: B2

Fairphone 5 supports these bands:

• 5G: n1/2/3/5/7/8/20/28/38/41/48/71/77/78
• 5G,ER: n66
• 4GLTE: B1/2/3/4/5/7/8/12/20/28/32/38/40/41/42/48/71
• 4GLTE,ER: B66

It looks like the Fairphone 5 covers T-Mobiles 5G Frequency Band 1 frequencies (bold), but Frequency Band 2 is not covered (italic).

Regarding 4G, the Fairphone 5 covers all LTE networks (bold) except for extended range band B25 (italics).

it doesn’t support US bands for TMobile

It covers some, but not all.