Converting MSX2+ RGB output to HDMI signal -- How?

I have good luck with OSSC (it does indeed output HDMI these days though in some of the earliest models it was DVI instead for reasons of licensing cost reduction I believe)

I didn't like the open sides of the CNC case because too much dust got inside, but I've been quite happy since I switched to this 3D printed one: https://laserbear.net/shop/ols/products/ossc-case/v/OSSC-EN-WHT

I think there are other 3D printed OSSC cases available too but I haven't tried them

I have also used MSX computers with the RetroTink 2x SCART for upscaling, but the OSSC produces a much better signal for my HDMI display and with more flexibility in the options. Specifically the OSSC can upscale with pillarboxing so the MSX display aspect ratio is preserved even on an HDMI display that won't do pillarboxing itself. Also it has a scanline simulation that actually works really well for interlaced MSX2 video modes. And finally it has multiple inputs so you can wire up MSX and V9990 at the same time and toggle between them using the remote, though for this I recommend getting an audio splitter so you won't lose sound when switching inputs (separate analogue sound system fed directly by the MSX works too of course)

I have one and it has been quite handy, it works very well using a DIN-to-SCART cable with my Panasonic FS-A1WSX (and other old non-MSX stuff, too). The first batch of production devices had three capacitor with wrong values and produced some halo; I got one of those early ones and swapping capacitors C54, C55, and C56 to 47pf ones fixed the issue. Some info on that here:

https://twitter.com/WobblingP/status/1554964039247306755

Allegedly, the devices being sold now come from the factory with capacitors of correct values and no longer have the halo issue.