Can i add 8 tb storage to my acer predator helios 300 ph315-55’s m.2?

Just in addition to the above and my experience with large drives, as the theory of windows OS is as follows. The governing factor for adding any drive that is larger in capacity than 2TB in a Windows OS is the format and the laptops bios, your Predator Helios 300 PH315-55 is a GUID (GPT) type format that has an infinite capacity for its operation, the only format that is limited to any capacity limit is the MBR/Legacy that has a max of 2TB capacity.

With adding a 2.5" 8TB drive, your are limited to what is on the market and fo course price and budget, as I can't see any spinner HDDs of 2.5" SATA-3 at 8TB on the market, but there is are 2.5" 8TB SATA-3 SSD drives like the Samsung 870 QVO 8TB or in the interface of the M.2 PCIe 4x4 there are the PNY XLR8 CS3140 8TB PCIe 4.0 NVMe M.2 2280 and few more.

The Predator Helios has 2x PCIe Gen.4x4 slots and a 1x 2.5" SATA III slot, so you can purchase a 2.5 Samsung 870 QVO 8TB for storage that is around USD $470, while an M.2 PCIe 4x4 8TB like the SABRENT Rocket Q 8TB NVMe PCIe M.2 2280 or the PNY XLR8 CS3140 8TB PCIe 4.0 NVMe M.2 2280 are at around USD $1190, but and also remember that the boot SSD slot #1 in your laptop is the fastest slot of the two, as the 2nd SSD slot #2 is allot slower and will run at PCIe 3x4, this is what I have experienced with my Nitro AN515-56 laptop, where the SSD #1 slot boot M.2 drive runs at full PCIe 3x4 which is at 3600MB/s read/write and the 2nd M.2 slot runs at max 2400MB/s read/write with both drives being M.2 PCIe 3x4 and the same type of drives, and one of the quickest M.2 PCIe 3x4 drives tested, of the WD SN750 and the same drive in the 2nd M.2 slot runs considerably slower, so be aware of all that also.

What I would recommend that you do is this, get an M.2 quick PCIe4x4 boot drive like the 1TB Samsung 990 PRO 1TB M.2 2280 NVMe PCIe 4.0 SSD (as this is one if not the quickest PCIe4x4 drive around) and then for extended quick storage I would get the 8TB Samsung 870 QVO SATA III SSD drive.

Then clone your existing boot drive with Samsung's excellent Data Migration software, then do the clone, install the new Samsung 990 Pro PCIe4x4 into the 2nd SSD lost and clone your existing M.2 boot drive, then install the 8TB 2.5" drive, go to Disk Management in windows > and make it a primary drive > format to GUID (GPT) then give it a drive letter E (as you already got C & D drive letters with the 2x M.2 drives), as upgrading in this way will give you a total capacity of 9.5TB if you add a new 1TB PCIe4x4 and use the oem 512GB M.2 Acer supplied boot drive in SSD slot #2 and add the 8TB new SATA III SSD drive. If you want to add more data then you can have the 2x M.2 slots with 8TB and the 2.5" SATA III which will give you 24TB total capacity, which will cost you USD $2,850 for 3x 8TB = 24TB which is USD $118.75 per 1TB which is about the right price of what a 1TB drive M.2 costs today. Good luck and hope this helps you out.