Hi Olli
Thank you very much for taking the time to help out 
So I am back on Manjaro now - profile is updated with relevant info and the outputs of uname -r and inxi can be found in the end of the post.
So what I have done is that I tried to install the driver as described here on Linux Mint 20.3. It worked as well as the author described, but at least now I know that it can work.
On Manjaro I have installed the 5.4 kernel, chosen it from the GRUB menu and installed the headers for 5.4.
Now when I try to install the driver I get this output:
linux kernel headers not found in /usr/src:
Debian (eg Ubuntu): /usr/src/linux-headers-5.4.173-1-MANJARO
Fedora: /usr/src/kernels/5.4.173-1-MANJARO
assuming the linux kernel headers package is not installed
please install the appropriate linux kernel headers package:
sudo apt install linux-headers-MANJARO
When looking the /usr/src it is empty, so I guess that is why the script will not install it. Then the problem is, where are the header files located in Manjaro? Further should the install script be changed to reflect the new location? Or can we create a symlink to the correct location from /usr/src? Or I am missing something very basic?
Hope you can help out
uname -r:
5.4.173-1-MANJARO
inxi:
System:
Kernel: 5.4.173-1-MANJARO x86_64 bits: 64 compiler: gcc v: 11.1.0
parameters: BOOT_IMAGE=/boot/vmlinuz-5.4-x86_64
root=UUID=6f7d5ee1-e56e-411c-93c8-39dbb7a74835 rw quiet apparmor=1
security=apparmor udev.log_priority=3
Desktop: KDE Plasma 5.23.5 tk: Qt 5.15.2 wm: kwin_x11 vt: 1 dm: SDDM
Distro: Manjaro Linux base: Arch Linux
Machine:
Type: Laptop System: Apple product: MacBookPro14,1 v: 1.0
serial: <superuser required> Chassis: type: 9 v: Mac-B4831CEBD52A0C4C
serial: <superuser required>
Mobo: Apple model: Mac-B4831CEBD52A0C4C v: MacBookPro14,1
serial: <superuser required> UEFI: Apple v: 447.40.12.0.0 date: 09/25/2021
Battery:
ID-1: BAT0 charge: 18.3 Wh (48.8%) condition: 37.5/54.6 Wh (68.7%)
volts: 11.0 min: 11.4 model: DSY bq20z451 type: Li-ion serial: N/A
status: Discharging cycles: 379
Memory:
RAM: total: 7.64 GiB used: 1.81 GiB (23.7%)
RAM Report:
permissions: Unable to run dmidecode. Root privileges required.
CPU:
Info: model: Intel Core i5-7360U bits: 64 type: MT MCP arch: Amber/Kaby Lake
note: check family: 6 model-id: 0x8E (142) stepping: 9 microcode: 0xEA
Topology: cpus: 1x cores: 2 tpc: 2 threads: 4 smt: enabled cache:
L1: 128 KiB desc: d-2x32 KiB; i-2x32 KiB L2: 512 KiB desc: 2x256 KiB
L3: 4 MiB desc: 1x4 MiB
Speed (MHz): avg: 844 high: 1276 min/max: 400/3600 scaling:
driver: intel_pstate governor: powersave cores: 1: 700 2: 700 3: 700 4: 1276
bogomips: 18406
Flags: 3dnowprefetch abm acpi adx aes aperfmperf apic arat arch_perfmon
art avx avx2 bmi1 bmi2 bts clflush clflushopt cmov constant_tsc cpuid
cpuid_fault cx16 cx8 de ds_cpl dtes64 dtherm dts epb ept ept_ad erms est
f16c flexpriority flush_l1d fma fpu fsgsbase fxsr hle ht hwp
hwp_act_window hwp_epp hwp_notify ibpb ibrs ida intel_pt invpcid
invpcid_single lahf_lm lm mca mce md_clear mmx monitor movbe mpx msr mtrr
nonstop_tsc nopl nx pae pat pbe pcid pclmulqdq pdcm pdpe1gb pebs pge pln
pni popcnt pse pse36 pti pts rdrand rdseed rdtscp rep_good rtm sdbg sep
smap smep smx ss ssbd sse sse2 sse4_1 sse4_2 ssse3 stibp syscall tm tm2
tpr_shadow tsc tsc_adjust tsc_deadline_timer vme vmx vnmi vpid x2apic
xgetbv1 xsave xsavec xsaveopt xsaves xtopology xtpr
Vulnerabilities:
Type: itlb_multihit status: KVM: Split huge pages
Type: l1tf
mitigation: PTE Inversion; VMX: conditional cache flushes, SMT vulnerable
Type: mds mitigation: Clear CPU buffers; SMT vulnerable
Type: meltdown mitigation: PTI
Type: spec_store_bypass
mitigation: Speculative Store Bypass disabled via prctl and seccomp
Type: spectre_v1
mitigation: usercopy/swapgs barriers and __user pointer sanitization
Type: spectre_v2 mitigation: Full generic retpoline, IBPB: conditional,
IBRS_FW, STIBP: conditional, RSB filling
Type: srbds mitigation: Microcode
Type: tsx_async_abort mitigation: Clear CPU buffers; SMT vulnerable
Graphics:
Device-1: Intel Iris Plus Graphics 640 vendor: Apple driver: i915 v: kernel
bus-ID: 00:02.0 chip-ID: 8086:5926 class-ID: 0300
Display: x11 server: X.org 1.21.1.3 compositor: kwin_x11 driver:
loaded: modesetting alternate: fbdev,vesa resolution: <missing: xdpyinfo>
Message: Unable to show advanced data. Required tool glxinfo missing.
Audio:
Device-1: Intel Sunrise Point-LP HD Audio driver: snd_hda_intel v: kernel
alternate: snd_soc_skl bus-ID: 00:1f.3 chip-ID: 8086:9d71 class-ID: 0403
Device-2: Broadcom 720p FaceTime HD Camera driver: N/A bus-ID: 03:00.0
chip-ID: 14e4:1570 class-ID: 0480
Sound Server-1: ALSA v: k5.4.173-1-MANJARO running: yes
Sound Server-2: JACK v: 1.9.20 running: no
Sound Server-3: PulseAudio v: 15.0 running: yes
Sound Server-4: PipeWire v: 0.3.43 running: yes
Network:
Device-1: Broadcom BCM4350 802.11ac Wireless Network Adapter vendor: Apple
driver: brcmfmac v: kernel bus-ID: 02:00.0 chip-ID: 14e4:43a3 class-ID: 0280
IF: wlp2s0 state: up mac: <filter>
IP v4: <filter> type: dynamic noprefixroute scope: global
broadcast: <filter>
IP v6: <filter> type: noprefixroute scope: link
WAN IP: <filter>
Bluetooth:
Message: No bluetooth data found.
Logical:
Message: No logical block device data found.
RAID:
Message: No RAID data found.
Drives:
Local Storage: total: 113 GiB used: 21.25 GiB (18.8%)
SMART Message: Unable to run smartctl. Root privileges required.
ID-1: /dev/nvme0n1 maj-min: 259:0 vendor: Apple model: SSD SM0128L
size: 113 GiB block-size: physical: 4096 B logical: 4096 B speed: 31.6 Gb/s
lanes: 4 type: SSD serial: <filter> rev: CXS4LA0Q scheme: GPT
Message: No optical or floppy data found.
Partition:
ID-1: / raw-size: 112.65 GiB size: 110.32 GiB (97.93%)
used: 21.25 GiB (19.3%) fs: ext4 dev: /dev/nvme0n1p2 maj-min: 259:2
label: N/A uuid: 6f7d5ee1-e56e-411c-93c8-39dbb7a74835
ID-2: /boot/efi raw-size: 300 MiB size: 299.3 MiB (99.76%)
used: 288 KiB (0.1%) fs: vfat dev: /dev/nvme0n1p1 maj-min: 259:1
label: NO_LABEL uuid: F8C3-9E8A
Swap:
Alert: No swap data was found.
Unmounted:
Message: No unmounted partitions found.
USB:
Hub-1: 1-0:1 info: Hi-speed hub with single TT ports: 12 rev: 2.0
speed: 480 Mb/s chip-ID: 1d6b:0002 class-ID: 0900
Hub-2: 2-0:1 info: Super-speed hub ports: 6 rev: 3.0 speed: 5 Gb/s
chip-ID: 1d6b:0003 class-ID: 0900
Hub-3: 3-0:1 info: Hi-speed hub with single TT ports: 2 rev: 2.0
speed: 480 Mb/s chip-ID: 1d6b:0002 class-ID: 0900
Hub-4: 4-0:1 info: Super-speed hub ports: 2 rev: 3.1 speed: 10 Gb/s
chip-ID: 1d6b:0003 class-ID: 0900
Sensors:
System Temperatures: cpu: 31.7 C mobo: N/A
Fan Speeds (RPM): N/A
Info:
Processes: 173 Uptime: 40m wakeups: 5 Init: systemd v: 250 tool: systemctl
Compilers: gcc: 11.1.0 clang: 13.0.0 Packages: pacman: 1213 lib: 332
flatpak: 0 Shell: Zsh v: 5.8 default: Bash v: 5.1.16 running-in: konsole
inxi: 3.3.12