There are some guys running 4090s with lower settings in VR.
What's your actual resolution setting in the Oculus App? Specifically, what frequency/refresh rate (72/90/120 Hz, etc) and Resolution (ex. - 5408x2736 pixels)? The 1.0/1.1/1.3 number changes depending on frequency for my Quest 3.
What are your DCS VR tab settings? Start with Pixel Density set to 1.0. If you have GPU head room after solving your problem, maybe try 1.1 but you'll get more fidelity setting SuperSampling in ODT, OTT, OXRTK or Quad Views. Either way, try to only add SS with one of these methods.
Set FOV multiplier in Oculus Tray Tool or OpenXR Tool Kit to 0.85/0.85 and tweak up/down until you stop seeing black bars. You're losing FPS by rendering frames you can't even see.
Outside of that, try these DCS settings:
Resolution - Set to lowest setting possible. This is what's rendered on your external monitor that you don't see because you're in a headset. You can also create a custom game profile in Oculus Tray Tool and set this here to something like 800x600.
DLSS Perf/Quality - PERFORMANCE
Sharpening - 0.5 +/- (look and see what looks best when everything else is stable)
Textures - HIGH
Terrain Textures - HIGH
So... I'd rather have these both set to HIGH and all the other bells & whistles set to OFF, vs Degraded Textures with AI Civilian Traffic & super dense chimney smoke. Personal preference here, of course, but give everything below a shot before setting your Textures any lower.
Shadows - LOW or MED
Flat Shadows Blur - OFF
Secondary Shadows - OFF
SSS - OFF
Visib Range - HIGH
Civilian Traffic - OFF
Clouds - MED
Water - MED
SSAO - OFF
SSLR - OFF
Lense Effects - Dirt + Flare
Heat Blur - OFF
Clutter/Grass - OFF(0) to 350
Forest Vis - 70%
Forest Details - 70%
Scenary Details - 70%
Chimney Smoke Density - OFF or 1
Terrain Object Shadows - FLAT
Full Screen - OFF (may make a diff, may not)
Cockpit Global Illum - OFF
Few other tips:
Set DCS Priority in Windows Task Manager to HIGH
Create Windows Defender Exemption for DCS parent and User/Saved Games folders. (**This one hack makes network admins cringe)
Shut down all the BS background tasks and services (Messenger/Browsers/Reddit/Discord, etc)
Windows Automatic Updates: OFF