iPhone 7 is not connecting with LTE/4G

Dear all,

My iPhone 7 is not connecting with LTE/4G while this is enabled. Is stuck in 3G.

• The carrier does not have any issue and covers 4G. Other carrier doesn't help.
• LTE/4G covered in this area.
• Putting on airplane mode doesn't help.
• Resetting network settings doesn't help.
• Resetting iPhone fully doesn't help.
• Software updated (12.3.1).

Does anyone know what I could try now?

Thank you in advance!