Win 7 works fine with Ryzen.
Installation:
I think I installed it by imaging the SSD boot drive while it was attached via SATA to my FX system using dism/bcdboot. Integrated the AHCI driver via /add-driver. Then used PS/2 keyboard to install the rest of the AM4 drivers provided by AMD for Windows 7 and Ryzen, or maybe I just transferred the image from the FX system directly. idk
For NVME boot, I think using WinPEv10 would work. There is also this Windows 7 image updater that integrates the driver directly.
Performance:
There are no performance penalties at all. However, Win 10 does have optimizations when gaming on sub-standard/overloaded hardware. That said, unless you plan on gaming while at 100% background CPU load or with a GPU older than 6 years, that does not really matter.
Windows 7 versus Windows 10 1703 on FX and Ryzen (Level1Thread)
Updates:
The CEIP is optional in Win 7/8 so, even if the telemetry code has been backported, it is not active, although there are scripts to remove it available. Be sure to use WuaCPUFix to fix Windows Update btw.
Conclusion:
In other words, it takes some time to set up, but otherwise works normally. MS removed accessibility features from Windows 8+, so Win 7 is still the only usable Windows OS for me.