I had an external SD drive 1T with files, time after I started using it with time machine, but then I tried to access the old files in the SD but they dissapeard, Im trying to get them back, but when I connect my hard drive only time machine appears

More than likely Time Machine destroyed any files located on the SSD (I'm assuming an SSD since an SD Card is not a good option for a backup) since TM will erase the drive so the drive can be utilized for backups. While technically it may be possible to point TM to a partition or APFS volume beside the data volume, this is a terrible practice.

FYI, once an SSD has been erased....even a simple erase....there is no way to recover data from that SSD due to how SSDs work.

Review this Apple article which has information about Time Machine:

Use Time Machine to back up - Apple Support

Think HWTech has it right.

When you tell Time machine to use a drive it ASKS you for permission to Erase the drive for the use of Time Machine. (Please supply your Admin password.)

That erasure from exFAT or other original format to current preferred APFS likely wiped out those files, unless those files were added AFTER the Time Machine erasure.