The Strike Industries Slide MRDS Adapter Plate is only compatible with the Strike Industries P365 slide, it will not work with a Sig OEM P365 slide. You would need the Evolution Gun Works Trijicon RMR Sight mount, which can be found by using the link below:
https://www.opticsplanet.com/evolution-gun-works-trijicon-rmr-sight-for-sig-p365-optics-ready.html
The Strike Industries Slide MRDS Adapter Plate only works with Strike Industries P365 slides. You would need the Evolution Gun Works Trijicon RMR Sight mount (linked below) if you want to install an optic with the RMR footprint. Unfortunately, you will not be able to utilize your rear sight.
https://www.opticsplanet.com/evolution-gun-works-trijicon-rmr-sight-for-sig-p365-optics-ready.html
The Strike Industries Slide MRDS Adapter Plate is only compatible with the Strike Industries slide for the P365. It will not fit Sig OEM P365 slides.