Summary: Manjaro boots into a blackscreen and hangs indefinitely on T14 Gen 6 Thinkpad. This is because Lunar Lake Intel graphics (<1 year old at the time of this post) are not supported by current LTS kernel / firmware on Manjaro.
Temporary solution / workaround: boot with nomodeset
kernel parameter OR use a non LTS kernel. e.g. 6.15.
For fellow newbies: