might be a silly question but on Kali Linux default SSH keys should be changed for security, is this something I need to do with Manjaro?
Manjaro does not ship with any default SSH keys, what are you referring to specifically?
AFAIK the SSH keys in /etc/ssh are automatically, safely generated on install.
You can regenerate them if you want; but (IMO) it’s pointless…the same software that generated those ‘default’ keys will be used to generate the new keys.
If you don’t trust those ‘default’ keys, how can you trust new ones?
Mod note: Moving to Software and Applications