Killer Wireless 1650 on Ubuntu 18.04 doesn't work

I installed Ubuntu 18.04 on a Dell XPS 15 7590 with a Killer Wireless 1650 2x2 AX Wifi card, but impossible to connect to wifi, with the following message : No WiFi Adapter found.

I found this answer which seems to work for some people, but not for me... The solution need an internet connection, and this is the current problem.

(The link doesn't work for now, so I put a screeshoot of instructions)

So I cloned the repo from an another computer and transfer with USB stick :

$ git clone https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/backport-iwlwifi.git

I installed make from the ubuntu iso, as Bernard advise here.

I continued to follow instructions :

$ make defconfig-iwlwifi-public
$ make -j4

Those commands seems to work, I only get the following message for both, at the beggining:

make[5]: execvp: ./lxdialog/check/lxdialog.sh : Permission denied
make[5]: execvp: ./lxdialog/check/lxdialog.sh : Permission denied

And when I finally enter $ sudo make install I got this message :

Building modules, stage 2.
MODPOST 6 modules
INSTALL /home/remi/wifi/backport-iwlwifi/compat/compat.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:72
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:79
sign-file: certs/signing_key.pem: No such file or directory
INSTALL /home/remi/wifi/backport-iwlwifi/drivers/net/wireless/intel/iwlwifi/iwlwifi.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:72
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:79
sign-file: certs/signing_key.pem: No such file or directory INSTALL /home/remi/wifi/backport-iwlwifi/drivers/net/wireless/intel/iwlwifi/mvm/iwlmvm.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:72
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:79
sign-file: certs/signing_key.pem: No such file or directory
INSTALL /home/remi/wifi/backport-iwlwifi/drivers/net/wireless/intel/iwlwifi/xvt/iwlxvt.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:72
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:79
sign-file: certs/signing_key.pem: No such file or directory
INSTALL /home/remi/wifi/backport-iwlwifi/net/mac80211/mac80211.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:72
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:79
sign-file: certs/signing_key.pem: No such file or directory
INSTALL /home/remi/wifi/backport-iwlwifi/net/wireless/cfg80211.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:72
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:79
sign-file: certs/signing_key.pem: No such file or directory DEPMOD 5.0.0-23-generic
Warning: modules_install: missing 'System.map' file. Skipping depmod.
make[1]: execvp: ./scripts/blacklist.sh : Permission non accordée
Makefile.real:104: recipe for target 'install' failed
make[1]: *** [install] Error 127
Makefile:40: recipe for target 'install' failed
make: *** [install] Error 2

Please, what can I do ? If I buy a USB to LAN adapter, can I have a connection ? Or it will be the same ? I can't found any solutions.

EDIT:
I finally bought a USB-C to LAN adapter, and I can have an Internet connection. I updated and upgraded packages, and I repeated again all the commands, but it still doesn't works. The sudo make install still display ssl errors, but not the make install error anymore.
What am I missing ? What can I do, please ?

I finally suceedeed, so I summarize the detailed instructions, hoping it can help some people.

1. Apparently it's important to turn off your secure boot before the following actions.
2. To fix the No Wifi Adapter found, you need a Internet connection. If you have an Ethernet port on your laptop it's good, else, you have to use an adapter. Personnaly I used a USB-C to LAN adapter and it works.
3. Once you have a connection, you can update and upgrade packages (Maybe not necessary, but always good) sudo apt update && sudo apt upgrade.
4. Execute all of the commands on this article:

sudo apt-get install git
sudo apt-get install build-essential

git clone https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/backport-iwlwifi.git
cd backport-iwlwifi
make defconfig-iwlwifi-public
make -j4
sudo make install

sudo git clone git://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git
cd linux-firmware
sudo cp iwlwifi-* /lib/firmware/

5. Before reboot, execute this command to update initramfs update-initramfs -u.
6. Now you can reboot.

You should be able to access wifi parameters now.
Thanks.