Can I use this to change my differential oil 2013 BMW 335i xDrive F30

Yes, so long as you do not have a limited slip differential in the rear, would be 600ml in each differential.

Is this suitable for a 2016 BMW 428ix Convertible Front Differential fluid change?

No, in your application you would need part number 83 222 41 35 11 listed below in a GL-5 https://www.fcpeuro.com/Parts/?keywords=83222413511

Does this fit Mercedes C250 2012 Coupe Base model rear wheel drive 1.8L?

On this model, for the rear differential the correct oil would be 001989330309 listed below. https://www.fcpeuro.com/products/mercedes-gear-oil-001989330310 As this fluid can also be used in manual transmissions, were you looking for manual transmission fluid I would recommend part number 50204 for a manual transmission. https://www.fcpeuro.com/products/manual-transmission-gear-oil-redline-83522-50204

2004 MB G500 Will this weight also work for the transfer case?

No, for your application you would need part number a GL-4, we recommend the Redline fluid listed below. 2.8 liters needed https://www.fcpeuro.com/products/gear-oil-manual-trans-red-line-50304

Compatible with 2016 340i RWD?

For your application we would recommend the redline fluid 75W85 listed below. https://www.fcpeuro.com/products/75w85-gl-5-gear-oil-1-quart-red-line-50104

Would this work for front and rear diff for 2011 bmw x5 35d?

Yes it would suit this application for the front and rear differential.

which gear oil would be best the Hypoid Gear oil or the GL5- Gear oil for the front axel of a 2006 BMW X5 4.4i

This would be compatible.

Is this perfect fluid to change on front & rear differential on 2018 VW Atlas SEL R-line

This would be suitable for the front differential only.

Would this work for front and rear differential for a 2013 X3 Xdrive35i? And how much would I need for each?

Yes - 3L total would cover both F and R.

Can I use this for manual transmission fluid change?

This can be utilized in manual transmissions, differentials, or transaxles.