Hello,
We'll get back to you on the original question here too, so everyone can read along. :)
No, the backrest must not be removed from this seat - the seat was built, tested and approved with the backrest. It has not been tested or approved with the backrest removed. When it comes to car safety, we recommend that you always follow the manufacturer's recommendations and, if in doubt, consult the owner's manual.
On our website you will find the operating instructions for every Joie product as a PDF:
https://chde.joiebaby.com/manual - if a link does not work, simply contact us via the web widget and we will be happy to send you the PDF!
Kind regards
Team Joie Switzerland