@Graycot Regarding FLOSS smartwatches, what do you think of the PineTime from @PINE64? You might be interested in having a look at the wiki.
https://www.pine64.org/pinetime/
https://wiki.pine64.org/wiki/PineTime#Datasheets,_Schematics_and_Certifications
BangleJS seems to be a similar project.
A more DIY approach might be Open SmartWatch (as in print your PCB and case).
https://open-smartwatch.github.io/
https://www.makerfabs.com/open-smartwatch.html
Related is AsteroidOS, which runs on proprietary hardware.
@floppy @Graycot @PINE64 I have the pinetime from pine64 and for the price its a great watch. Its not the best watch but its not at all slow. There is not one time where any part of the ui gets slow or anything. The os is made really good for the low hardware and they try to not put so much things in the os that will use up the storage/ram