I did my research. At the time it was new and I asked a lot of questions at the Apple Store before I made the switch.
With Apple's documentation you need to read between the lines. The support documents tell us, what will be working, but rarely, what not will be working. So it is very hard to search for limitations and unsupported features.
For example, the iCloud documentation promises, that the photos, videos, Moments, Collections, and Years and all of your Memories and People are updated everywhere. But nowhere is mentioned, that albums or even smart albums will sync. https://support.apple.com/en-gb/HT204264
iCloud Photo Library automatically keeps every photo and video you take in iCloud, so you can access your library from any device, anytime you want. Any changes you maketo your collection on one device, change on your other devices too. Your photos and videos stay organized into Moments, Collections, and Years. And all of your Memoriesand People are updated everywhere. That way you can quickly find the moment, family member, or friend you're looking for.
The document describing how iCloud Photo Library will sync between Macs mentions the albums and smart albums, https://support.apple.com/en-us/HT204486
So we can be sure, that the smart albums will sync to iCloud. And this document is one of the few documents that are describing the limitations in detail and lists the items that will not sync between two macs.