Gorgeous bike indeed!
I have to admit I was surprised to see the RD-RX817 and a front derailleur - Shimano say the RD-RX817
can not be used with a front derailleur ;-)
[edit] so I had a quick look on some Shimano pages and found this:
The RD-RX817 is a clean-slate 1x-only rear derailleur. Its total chain capacity is less than the RD-M8050-GS because the XT derailleur was designed to work on either a 1x or 2x mountain drivetrain.
The specification page on si.shimano.com says this without saying it explicitly. The 31t total capacity is just enough to handle the 11-42.
Attempting to run a 2x11 setup with a 40 or 42 tooth large cog will give reduced shifting quality and may result in damage or injury.
Still, it clearly works for you, so enjoy ;-)