Ugreen 4300+ HDD and SSD?

I've recently bought a UGREEN NASync DXP4300 Plus and currently have 2 × 8TB HDDs running in RAID 1.

I've been given a brand-new 1TB SSD, and the manual suggests that the NAS supports SSDs as well as HDDs.

Can I install the SSD alongside my existing HDDs without compromising my RAID setup or the reliability of the NAS? Ideally, should I put the operating system and apps on the SSD?

Cheers very much