Interestingly, Monzo takes a few seconds (~5) to notify me of a transaction if I do it in Germany. UK, Belgium, Malaysia and Indonesia are all instant.
I assumed that there must be some further process that it goes through, between telling the credit card reader that it is completed and Monzo getting informed.
I wouldn't muddy the waters here with talk of Monzo. Most chip reader cards don't do what Monzo does in terms of real-time backend transaction verification, that's a generation further than the stuff being rolled out in the US.
Correct. Cards can indicate whether they need to be verified online or not. Most do not require this (so transactions are just recorded and processed some time later), apart from Visa Electron which was designed for under 18s, and therefore does not have an overdraft, so requires an online balance check.
Monzo take advantage of this to enable their realtime notifications and related features, otherwise Monzo would receive the notification of the charge up to 48 hours later which would be a significant harm to the UX.
I assumed that there must be some further process that it goes through, between telling the credit card reader that it is completed and Monzo getting informed.