Exactly, I had to do the same and have measurably increased the reception. The problem for me is the building and the location of the Predator Connect. I used a TS9 to SMA connector, a window feed-through and an external antenna.

Frankly, I still don't know if it's worth putting a 5g antenna outside, after my first tests (antenna only outside, not fixed and not exposed at best) I get nothing more. Du coup j'hésite à acheter rallonge pour la fixer sur le toit(100 chf de plus) antenne 80chf plus adaptateur or pour la conversion sma/ts9 20 chf.
I think I'll look on wish for a cheap extension lead if I get a better performance, in case if positive I'll buy a better quality extension lead.

Did you use a Y Type Sma Female To 2 X Ts9 Male Plug Splitter to use both Ts9 slots?

Sorry, I can't tell you that either.
But I think it should be mentioned in the product description, if that is even possible.