How long after silhouette lift/thread lift to resume sexual activity/kissing?

Great question! This is my “take”.
Silhouette InstaLift (SIL) is a PLLA (collagen stimulating) thread with “traction” cones. It:

Passively suspends the filamentous network of the face by pulling the cones upward and anchoring them in position while
Actively stimulating collagen formation (which takes 3 weeks and more for sufficient holding power) to keep them in place.
Depending on the technique of the “injector” and number of sutures placed, there will be more or less holding power until collagen formation takes over to heal and contract the engaged tissues.

More activities which pull the sutures or pulls the surrounding tissues will displace/release the cones and diminish the effect of the passive tissue elevation.

So, active rotation of the face will pull on the sutures on one side and compress the sutures on the other side possible releasing the desired pull. Blowing, kissing, sucking and other activities may displace the cones as well. There is a spectrum of loving and sexual activity. Without getting into details, I hope you will understand how your investment in a meaningful minimally invasive procedure may be diminished with overly animated activity during the first 3 weeks following SIL.

I hope this has been helpful. All the best!