Hello,
Because of the end of support of Hassio as a native Synology package due to Docker version, I opened a ticket to Synology support.
The answer is :
We have planned to update Docker to 20.10 in the second half of this year while the release date will depend on our resources and product strategies, etc.
Will make hassio supported again with fredrike native syno package ?
No, I don’t think so. There were multiple issues with running hassio as a Synology package and I don’t think just upgrading Docker will enough.
Check the original thread and make a list of things that people reported as issues and we can have a look. But at the end of the day I think you are better of investing the $100 on a PI and run hassos from it.
Ok, what a pity 
As long as it works with influxDB, i can still use it.
But I’m looking to migrate to HA Core with Docker container.
And I’ll try the VMM Hassio alternative since I have 8GB RAM.
It still wouldn’t be officially supported - so any future change in HA could potentially break it.
Docker version was just one of 3 or 4 things that made hass.io unsupported (if I remember correctly).
I tried the VM method.
It works, but my DS216+ 8GB is not sized for that. CPU load 100% when the VM is running under VMM.
Remains the Core method that I tested (thanks again bearderTinker :))
I’ll be ready to migrate from this native package to Core when it will not work anymore.
And thank you also fredrike for the native package 
I just moved my setup to VMM this weekend on new machine. So TBH hass.io package was still working for me. Although I had to remove most of addons.