There are multiple AT&T Carrier Profiles which can be referenced in the KBA I shared:
If you set manually using Generic and you are using a 5G tablet plan (for example) you would enter ‘nrbroadband’, if the plan is not provisioned for 5G then it would be ‘broadband’. The IP Type should be IPv4v6. In order to connect to AT&T 5G bands you would need to ensure your plan is provisioned for 5G access. For this AT&T needs the plan to be activated using an approved 5G device IMEI. If this has already been done then the InvisaGig would need to be configured with this same IMEI. You can type ‘REPAIR’ (all caps, no quotes) at the Main Menu to enter this if you have not already.
If the InvisaGig has already been correctly configured for 5G access (by setting the appropriate APN and IMEI) and the plan is provisioned for 5G access by AT&T you should then have the ability to connect to 5G bands if they are available on your tower. You can check cellmapper.net to see if 5G bands are available in your area. Be aware that this site is crowd-sourced and not official so it may not be 100% up-to-date and accurate, but it historically provides a fairly good idea of what is available in most areas.