I get LTE only mode option on my Samsung Galaxy On8 with 1 SIM CardInserted or using a 4G only Network Operator like JIO. Samsung has disabled the default code to enable 4GLTE only mode but I’ve figured a way to enable LTE only option using an application called Network Mode ( Developer name - Ather Akber) . You can search it on the Play Store. The only downside is that, it can only enable 4G LTE mode on the first SIM. If anyone knows a way to enable 4G LTE Mode on both SIM cards ( 1 SIM at a time) , then please post the process here.