If it installed the first time and is not installing the second time, the SD card is either fake or simply does not have enough room. Remember that you need double the space of an .NSP to install it.
No, 4.X firmwares have 5 fuses burnt while 5.X firmwares have 6.
Even though I myself highly doubt its patched, follow this guide so we know for sure where the problem might lie:
https://gbatemp.net/threads/a-defin...atched-or-not-purchases-after-07-2018.512018/
The Switch does not support exFAT out of the box. It needs the exFAT update in order to read exFAT formatted SD cards. If the 128 GB SD card is exFAT formatted and is inserted, but you don't see a prompt to download the exFAT update, it sounds like the card is fake.