Joseph, the optic that you are asking about will not fit directly onto the Glock 43x. You will need to buy an adapter place such as the DPP Titanium Adapter Plate as the Holosun optic has the Holosun K Series footprint, which is a "Modified RMSc footprint"..

Hi Joseph, no sir, this will not mount directly to the slide. (unless you file down the rear recoil lugs on your optic cut completely).
The Glock 43X MOS comes from the factory with an optic-ready pistol slide designed to accept optics with the Shield RMSc footprint. However, its optic cut uses both front and rear recoil lugs that will not allow you to mount a Holosun K optic directly to the slide.
Also, the G43X with the Modular Optic System (MOS) does not come with adapter plates.
The adapter plate you would need is here >>> https://freedomgorilla.com/collections/glock-slim-43x-48-mos-adapter-plates-for-optics-ready-models-only/products/glock-43x-48-mos-adapter-plate-for-holosun-407k-507k
Stay safe & have a great day!

Which holosun for Glock 43x MOS?
This means it has four recoil lugs, two in the front and two in the rear. The optics we recommend are the Holosun 407K, 507K, and EPS Carry.

Hi Joseph and welcome. Yes Sir, the The Glock 43X MOS and G48 MOS have an RMSc footprint and this will mount direct to the slide. Cheers, stay safe and enjoy! ----- https://freedomgorilla.com/blogs/news/best-glock-g43x-g48-mos-holosun-optics-adapter-plates#:~:text=What%20footprint%20is%20the%20Glock,%2C%20507K%2C%20and%20EPS%20Carry.