Is there a way to clone Linux SSD to another one while still being fully bootable?

Like clone it while the OS is active and not shutdown?

I wrote a P2V app about ten years ago that keeps an incremental sync of a prod, in-use filesystem, with the final cutover requiring a full shutdown and rescue boot. You can minimize downtime, but to be 100% safe, I don't think it can be completely eliminated.

Yes

Clonezilla can do it and is even user friendly.