Not the best way to start your Linux journey. If you really want to use a removable device please read these articles
- https://archived.forum.manjaro.org/t/howto-run-manjaro-on-a-stick/109520
- [root tip] [How To] Do a manual Manjaro installation
- Manjaro XFCE 20.0.3 - Persistent USB - released
Installing to a removable disk has some challenges - especially with booting - which may explain why you are dropped to a rescue prompt.
It is impossible to deduct what is stalling for you some ideas is - I have not thought any of them through - so take them for what they are - just ideas
- your boot is mounting the device by name e.g. /dev/sdy1
- grub is on your internal device and the external is not powered at boot time
- your external device is cached and due to cache not flushed data becomes corrupted when tlp powers down your usb devices.