SMART data self test is greyed out in Disks?

Why is that? It is ok for the 2nd drive which is external usb ssd.

From How can I check the SMART status of a SSD or HDD on current versions of Ubuntu 14.04 through 18.10?:

SMART option greyed out

This can happen with NVMe SSD's. You need to install NVMe SSD specific SMART tools:

sudo apt install nvme-cli

Then run the program to report health of drive:

$ sudo nvme smart-log /dev/nvme0
Smart Log for NVME device:nvme0 namespace-id:ffffffff
critical_warning                    : 0
temperature                         : 40 C
available_spare                     : 100%
available_spare_threshold           : 10%
percentage_used                     : 0%
data_units_read                     : 28,167,888
data_units_written                  : 19,397,424
host_read_commands                  : 561,183,142
host_write_commands                 : 171,788,833
controller_busy_time                : 1,354
power_cycles                        : 2,385
power_on_hours                      : 1,363
unsafe_shutdowns                    : 133
media_errors                        : 0
num_err_log_entries                 : 608
Warning Temperature Time            : 0
Critical Composite Temperature Time : 0
Temperature Sensor 1                : 40 C
Temperature Sensor 2                : 51 C

The most important data point is:

percentage_used                     : 0%

When it hits 100% it is time worry about replacing your drive. That said this drive is two years old and still at 0%

Not all USB adapters support SMART. I have 2: one of them supports it, the other one not. Both of them USB3