Recently, customers have been receiving email alerts issued by the Carrier Optus that the 3G network will be being shut off by October 28th 2024. These warnings are sent to ensure that customers are aware of the impending changes and to encourage them to transition fully to the LTE (4G) network. By default, Mikrotik devices are set to receive GSM and 3G signals as well as LTE, so if these are not disabled they will attempt to use those services as fallbacks, which therefore give them the emails warning them the 3G is being shut off (since it is still being "used"). Disabling 3G on Mikrotik devices will help users avoid disruptions and take full advantage of the superior performance and reliability of the LTE network being offered.
To disable 3G on a Mikrotik Device, choose the Interfaces List, then select LTE Interface.
Before touching anything, make sure to set an APN in "LTE APNs". Each ISP carrier has their own APN available on their website.
Once an APN is set, double click on the LTE interface.
Find the "Network-Mode" setting. You should be able to select which modes you'd like the LTE interface to operate with, LTE only or all modes.
Disabling the 3G allows Optus customers to enjoy better coverage, faster data speeds, more reliable connections and future proof devices against upcoming network changes as Optus plan to phase out 3G towards the end of October 2024. This step by step helps customers stay up to date with the latest Network standards (4G and 5G).
Ref https://help.mikrotik.com/docs/display/ROS/LTE for more info.