Windows – Can’t install Windows 10 on Samsung 850 EVO (250GB) SSD in Asus K75VM

I recently decided to revitalise my old Asus K75VM laptop (± 7years old now) by switching from the original (broken) HDD to a Samsung 850 EVO SSD, and I'm at a loss.

I've been trying to install Windows 10 on it (legal version, from bootable usb, clean install), but it doesn't seem to work, no matter what I try.
Here's what I've done so far (with no success):

• used the included software (Samsung Magician, Samsung Data Transfer) to copy everything from the intenal hdd to the ssd and then switching them out (no bootable device detected)
• formatted the ssd (gpt by default) without creating any new volumes (no bootable device detected)
• formatted the ssd (gpt by default) with a single primary partition (ntfs, no volume letter, same result)
• formatted the ssd (gpt by default) with multiple partitions (same result)
• formatted the ssd from the Windows 10 installer (can delete and create partitions, but not use any of those partitions to install Windows 10 on, got a message that the device should be formatted with gpt insteqd of mbr, which was already the case)
• formatted the ssd to mbr with no partitions created (no bootable device found)
• formatted the ssd to mbr with a single primary partition (ntfs, no volume letter, same result)
• formatted the ssd to mbr with multiple partitions created (same result)
• fromatting the ssd from the Windows 10 installer doesn't work

I've also tried switching the ssd to the other slot (the latpot has 2 internal hard drive slots, for more info: Asus K75VM specs) and when in the second slot, I got it to work once, but after I tried to install it in the primary slot every other attempt, no matter which slot, it failed (contacted Asus about this and they said it matters which slot you put it in and the ssd (used as primary drive) should be inserted in the laptops primary slot and an optional additional hard drive can be inserted in the secondary slot).

How can I install Windows 10 on this ssd? It should be compatible with my laptop, but I'm barely familiar with ports, connectors and motherboards and such, so I wouldn't know.

If you know what I'm doing wrong and know the proper way to do this, please be as detailed as possible (step by step (how to format, how many partitions to make, …), if possible), so I can get this laptop back up and running again.

So many thanks to whoever can help me out.