Same here. I just got my note 10 plus unlocked yesterday and moving the SIM card from the note 9 T-Mobile branded to this unlocked 10 plus has killed my signal. I get full bars almost everywhere that I go with the note 9 and I get one bar and sometimes no bars in all the same places with my unlocked note 10 plus. I've seen other people complaining about this online and nobody has any idea why this is happening..
I have got my Galaxy Note 10Plus in pre-orders switched from iPhone XS Max but very disappointed all other features are great but 4G signals are very poor frequent disconnections. Normal mobile call get disconnected or broken voice. At the same places I was using my iPhone and signals were great. Even I have changed a sim card but same problem. I am using STC in Saudi Arabia.
Its not about carrier they have excellent service at same place I was using iphone and having good reception. I think there is something wrong with note 10 plus as other users also reported same issues.
@userRXRHBLAlgm Have you tried clearing the cache partition on your phone? If not here are the steps on how to clear the cache partition on your phone.