Yes you can add a folding or retractable BRACE. I'm sure that's what you meant, as this is classified as a pistol
Folding brace in stock here
joeboboutfitters.com/HB-Industries-SB-Tactical-Folding-Brace-Assembly-p/stribog-sbtstribog.htm
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Another in stock here
https://a3-tactical-inc.myshopify.com/products/modular-side-folding-arm-brace-stribog
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This version comes with the collapsible brace
https://kinglerweaponstore.com/product/grand-power-stribog-sp9a3-9mm-pdw-with-tailhook-brace/

Rommell, you can add a Folding Brace without changing the classification from a handgun to a Short Barrel Rifle. https://hbindustries.net/store/shop/stribog-bt-type-stock-brace-adapter-sbt/

Adding any type of stock to this would make it into a short barrel rifle (SBR) which is a Class III weapon and all NFA rules will apply. You would have to find an Class III FFL dealer and go through the process, $200 tax, finger prints, paperwork and ultimately wait for it to come back. You could add a brace which does not qualify it as an SBR.