Do i understand correct in the first place? You are using the same sim card when put on the phone, you get ultra 5g, but on the tp link, you only get NSA? To me this doesn't make sense at all. Because since this is home 5g, you should be getting consistent connection, which is ultra 5g. Tp link you can't just set to 5g only, because for nsa to work it needs 4g for b28. And 5g for n78. With your tp link, either you upgrade the firmware or call um to ask them rectify for you.

No in my phone i am using a different umobile hp prepaid/postpaid sim, uhome5G sim i never used in my phone. So basically 2 different sim. Only on my phone it could connect to Ultra5G, but uhome5G in router die die won't connect.
Makes me think that umobile purposedly doing that on purpose.

you should call UM to verify this matter, does uhome sim support Ultra 5G? anyway, the fastest verification is to put your uhome5sim to your phone to test, if its get ultra5G, means your tplink is having problem wor !