Cannot use screen Mirroring on MacBook Pro 2013

can not find the hint to upload a new device, use the same wifi (use vpn), the same Apple ID, open bluetooth and everything else, I cannot find the the "add device" point at the bottom( the left one); Try to attempt every tutor methods on social media. I found that my computer has the highest system, nothing went wrong except this.

[Re-Titled by Moderator]