I have this posted in the UB820 thread but figured I should cross-post here as well.
I previously posted a guide very similar to this aimed at JVC projector owners, details on that here.
Panasonic UB420 / UB820 & SDR2020 (aka, the projector solution)
The Panasonic UB420 & UB820 are the
answer for physical 4K media. With the built-in SDR2020 Tone Mapping, 4K discs behave exactly like HD discs and you never have to deal with HDR shenanigans or titles looking 'dark'. The UB420/UB820 will make you think you bought a new projector. Configured with the settings below, your projector will not see a ‘HDR’ signal so it will not probably not switch to whatever Gamma curve your projector uses. The UB820 is still interpreting the HDR data off the disc and sending a ‘full range’ signal to the projector so you are not leaving any color or brightness 'on the table'. You get beautiful high resolution and wide color gamut images without the hassle.
The UB420 or UB820 is worth every single penny and your only regret will be waiting this long to get it.
For projectors the UB420 & UB820 are functionally identical (420 doesn’t support Dolby Vision but neither do projectors). I even tested disc load times and streaming times. The UB420 & UB820 are identical. The only difference I could find was the UB820 has DV support and Optical Down Sampling goes to 192kHz on the UB820 and only 96kHz on the UB420. I only use HDMI so that doesn't matter either.
Panasonic UB420 / UB820 Optimal Settings for Projectors (SDR2020)
On the UB420 / UB820
Settings>HDMI>Advanced>HDR/Color Gamut Output>SDR/BT.2020
Settings>HDMI>Advanced>HDR/Color Gamut Output>HDR TV Type>Basic Luminance LCD and Projector
Settings>Audio>Settings for High Clarity Sound>Front Panel Display>Off (UB820 preference)
On the UB420 / UB820 During 4K Disc Playback
Options (remote button)>Video Settings>Optimum HDR Adjustment>HDR Optimizer>On (preference)
Options (remote button)>Video Settings>Optimum HDR Adjustment>Dynamic Range Conversion Adjustment>+4
to +8 (preference)
Regarding HDR Optimizer, you lose some brightness but gain detail in explosions and similar. I started with this off but now have it on. Dynamic Range Conversion Adjustment will depend a lot on your screen size, bigger screens will want more. I have left the other settings at defaults (so far).
On the Projector (JVC specific settings here)