Hi my scores are kind of low for CINEBENCH R20!! Single Core=418 And Multi Core=5162
Window 10 1909
Bios 1.20
Bios Setting Default 

Ya your multi core isn't to far off normal, but your single core does seem awfully low. 
 
According the this website that lists stock R20 scores, yours should be 461 and 5286. 
https://www.cgdirector.com/cinebench-r20-scores-updated-results/
 
Now scores can vary depending on setup and which bios you are on, if on a more recent one you may lose a bit of performance do to mitigation patches. Yours seems way to low though even for that to be the main issue. I am honestly not sure but definitely doesn't look right to me.

Definitely a little low. My old 4790K @ 4.2Ghz scores 401 in R20. Your 7900X clocks up to 4.3Ghz for a single core so it should be doing better.
 
You should use CPUZ and verify your RAM is running at the correct settings. Also use a temp monitor like CoreTemp to monitor the CPU while running CineBench to make sure it's not throttling for some reason. 

Temps are good but Volts are higher in some Cores!! None of the Cores are hitting 4.3Ghz except few times for Sec.  

Okay, I tell the story again that I've found with my investigations. Im really fresh x299 platform user. For me - all core all time overclock is old and dirty way of doing things - You don't need 99% time that and this makes your PC takes enormous amounts of power when idle and even worse - under load.

1) Step one - update your BIOS to the latest version, you have already done - https://forums.evga.com/BIOS-Updates-for-X299-Dark-120-FTW-K-121-Micro-ATX-2-113-Micro-ATX-122-m3013412.aspx
2) Take look at cpu_conf picture I have attached and set your values according to the instructions I've written in RED, leave others as they are in your bios screen. Save reboot. Do you now get better 1 core speed? I suppose you will.
3) Now take next steps to get even more speed from 1 core load. Take a look evga-percore picture I have attached and choose per-core overclocking and keep the values all the same at the left and at the right columns, like in YOUR bios (real values may differ than that in the picture). Try again benchmark
4) Try Mesh Ration setting of 30 - this should also increase speed.
5) Try loading memory XMP profile, if possible, from Bios Memory section.
6) Do you have Windows 10 installed automatically intel turbo boost max technology 3.0 application? Should be installed and "affinize only to cores with diversity" chosen under settings.
 
Now make sure you have Windows "High performance" power plan in use from Windows Control Panel "Power Options". Idle clocks may fluctuate and this is perfectly normal. Try now Cinebench R20 Multi and Single !
 

KrikU may be right though, could be a UEFI setting. If a single thread isn't clocking up to 4.3Ghz then that explains your R20 score. Most of today's scores are from the high boost clocks more than any actual improvement to IPC, so your chip losing out on 300Mhz hurts it a lot. 

The low score might be the new 1.20 BIOS packing cancer Intel micro-code. Not sure, but maybe switch to an older BIOS and see if the score moves up to where it should be.
 
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