I am not being able to see any current OS updates for my MacBook Pro

I have a MacBook Pro 2017 with current os Sierra , 10.13.6, I am not being able to see any current OS updates, tried everything available on the community, I am also not being able to backup my computer using time machine app. Any pointers on this are much appreciated.

Best,

Vinod

[Re-Titled by Moderator]