Hi, as it seems that this info is thin on the ground or spread around in bits and pieces.
first the G20CB is a PCIe 3 board so while there are very fast M.2 drives that use PCIe 4 you will likely not see the full speed they can deliver so, buying M.2 drives rated to be 3500 MB/s on PCIe 3 would offer better value and will work to there max rated speed*.
I added a standard Samsung 980 1T drive and the Samsung testing app says it’s running at max speed. I expect the 980 1T Pro also works. And if someone tests it they can report it to this thread.
next size it’s all over this forum that only 250gig M.2 drives will work, this is not true as far as I can tell any capacity you want will work, when doing a windows 10 fresh install, from a USB.
as above I know that a 1T Samsung 980 works as I installed one.
Doing the install.
this is my suggested method.
first an bios upgrade to the latest version from ASUS G20CB page, they have all the drivers and apps to get the case lighting working and all the last drivers if your unhappy with the windows ones.
next instal the M.2 drive ( I suggest a large heat sink is also fitted or heat sink and fan) I will come back to cooling later, and fan power options. If you need help to take your system apart there are videos of YouTube.
once done boot into bios and load optimised bios setting and restart, then go into bios again for the SSD drive settings leave the SSD driver running, but disable all the individual SSD drives including the CD. This is so you can tell what your installing onto in windows 10 setup.
Ok create a windows 10 USB, these you can create and they are free from Microsoft.
So insert the USB in a front port USB and reboot the system, this should boot to windows setup with nothing but the blank m.2 active and all other drives disabled.
you enter windows 10 setup select the drive which can only be the m.2.
and complete the install.
if you get an error at the drive selection screen. Drive error fix windows 10/11 https://youtu.be/ZnV7ZjDsgas
once installed you can go back to bios and reactivate the SSD drives, and save and reboot.
copy data from your old drive to your new m.2. Docs pics etc.
M.2 cooling yes it will need some big heat sink will help off the top of my head you have about 18mm above the m.2 drive to fit one maybe a little more.
there are lots of them on Amazon, some with fans some without.
if you want a fan (which I recommend) then powering that fan is your next problem.
option 1 (which I think is the best) if your happy to use the top slot for a single SSD drive so you only have the m.2 and CD and one other SSD the one above the CD then you can do away with the lower drive, under the graphics card.
this gives you the power out for that lower drive to power a fan or multiple fans.
fans they come in 2 power ratings 5v red black cable or 12v yellow black power cable.
this will tell you how to wire them up.
the SSD pin our on the G20CB is not standard pc it’s just standing pins it uses a 5 pin connector but has one missing so you can only fit the connector one way.
on the G20CB it’s, yellow, blank, red, black, black from memory, but the cable will tell you sorry no picture.
I used a 3 pin fan cable and soldered on individual pin female ends this lets me pick what the power is 12v or 5v by just swopping what pin I put them on.
this is the closest Amazon seem to have
on mine I made the connectors signal pin ones from an old pc desktop case these used to have single pin connectors.
if you buy one or make one you now have a full time powered fan, or fans if you make a splitter or again buy a fan power splitter. You can use the cable above but only as 5v as only the 5v and black are next to each other to use a double connectors like that.
option 2 if your only using one of the GPU power outs then it’s possible to pull power from that but only 12v.
anyone that seen these will know what I mean, not neat and checking the colour coding of the connectors on the six pin to the gpu socket to the cable to make sure they match is needed and it only gives you 12v.
option 3 make a splitter for the fan out on the motherboard.
https://www.amazon.co.uk/gp/product/B0BLGXT7C8/ref=ox_sc_saved_title_6?smid=AOXZIQW4RHZR1&psc=1 this is my best guess as to the size but they are 5 pin sockets on the motherboard very small, so I didn’t rate my chances of making my own fan splitter so went for option 1. Plus I didn’t know what wire was what, and you only want power and earth not any of the signal wires or you will confuse the motherboard.
Any questions just ask.