The checkbox in front of database name is greyed out. Unable to select the database for backup.

Beremote Debug Log from SQL Server-
BEREMOTE: [fsys\sql2] - Marking database SolarWinds unselecteable. Hekaton enabled.
BEREMOTE: [fsys\sql2] - AddToSnapshotSet called
BEREMOTE: [fsys\sql2] - Building device list for snapshot
BEREMOTE: [fsys\sql2] - In GetDeviceList for SolarWinds
BEREMOTE: [fsys\sql2] - file list query started
BEREMOTE: [fsys\sql2] - checking volume requirements for H:\MSSQL13.MSSQLSERVER\MSSQL\DATA\SolarWinds.mdf
BEREMOTE: [fsys\sql2] - adding device to list H:
BEREMOTE: [fsys\sql2] - checking volume requirements for I:\MSSQL13.MSSQLSERVER\MSSQL\Data\SolarWinds_log.LDF
BEREMOTE: [fsys\sql2] - adding device to list I:
BEREMOTE: [fsys\sql2] - checking volume requirements for H:\MSSQL13.MSSQLSERVER\MSSQL\DATA\SolarWinds_FG1.mdf
This issue is caused due to the Hekaton feature ( In-Memory OLTP) configured for the database..
The support for SQL In-Memory OLTP databases has been added in Backup Exec versions 21.2 R2.
Backup Exec version 21.2 R2 or later and updating the remote agent on SQL server should allow the selection and backup of In-Memory OLTP databases.