If you are experiencing very slow booting after installing manjaro linux (mine was around 10-15 sec), then do the following things:

BIOS Tweak

Legacy ROM

Diable Legacy Option ROMs

SMART Reporting

Disable SMART Reporting

TMP Security

Disable TPM Security

Secure Boot

Disable Secure Boot

Fast Boot

Set Fast Boot to Minimal

BIOS POST Time

Set Extended Bios POST Time to 0

Linux Tweak

1. This service you can stop, disable and mask by

   systemctl disable --now NetworkManager-wait-online.service
   systemctl mask NetworkManager-wait-online.service
   

2. If you don’t use any encrypted disks you also can stop, disable and mask lvm2-monitor.service:

   systemctl disable --now lvm2-monitor.service
   systemctl mask lvm2-monitor.service
   

3. You can stop snapd service

   systemctl disable --now snapd.service
   systemctl mask snapd.service
   

Hope you will have 1 or 2 sec boot time now :)