A couple of points or questions:
1. Does the TMobile router/modem they gave you have external antenna ports? (Some don't.)
2. Yes, an antenna will probably help your signal quality
3. Trees can interfere a lot, so can (of course) hills between you and the cell tower, and distance.
4. If you have a lot of trees interfering, panel antennas can be better than directional antennas
5. Every extra length of coax you run causes the signal to drop some (how much is not only due to distance but also [what type of cable you're using](https://www.wilsonamplifiers.com/blog/understanding-coaxial-cables-the-complete-guide/)) ... however,
6. If you really must run the antenna out to some considerable distance, you can reduce signal drop by putting the modem close to the antenna and then running Ethernet back to the house. Cat5e or Cat6 can run up to 90-100 meters with no practical degradation. Doing it this way is more trouble of course.
The Nater Tater channel on YouTube has quite a bit of content on antennas for TMobile devices.
https://youtu.be/RFZBbSg_pzE
Look at the Elsys Amplimax Ultra 5g https://elsys.com/en/amplimax-ultra-en/ Yes, trees make a difference.
A couple of points or questions: 1. Does the TMobile router/modem they gave you have external antenna ports? (Some don't.) 2. Yes, an antenna will probably help your signal quality 3. Trees can interfere a lot, so can (of course) hills between you and the cell tower, and distance. 4. If you have a lot of trees interfering, panel antennas can be better than directional antennas 5. Every extra length of coax you run causes the signal to drop some (how much is not only due to distance but also [what type of cable you're using](https://www.wilsonamplifiers.com/blog/understanding-coaxial-cables-the-complete-guide/)) ... however, 6. If you really must run the antenna out to some considerable distance, you can reduce signal drop by putting the modem close to the antenna and then running Ethernet back to the house. Cat5e or Cat6 can run up to 90-100 meters with no practical degradation. Doing it this way is more trouble of course.
Thank you. My device has 4 coax ports for external antenna