It truly is a small supply for the combined ratings of those circuit breakers but.... except for the workshop, all the other designated areas are not likely to draw much current.
TV, Study and Lights don't use much at all although nothing is really stopping you from plugging in a heater in the study, while using a grinder and boiling a kettle at the same time etc

...but its very unlikely, have you actually had any tripping?
As far as I know as long as the circuit breaker wire size ratio is correct it is compliant, but I'm continually learning new things in the sans book it seems!
What may have happened is that there initially was a larger circuit breaker on the supply side, the wire may have been too thin and the electrician who signed it off decided to put a 20amp circuit breaker in to make it compliant.
Looking at the picture though...it seems they may have used 4mm wire which means you could increase the circuit breaker size to 25/30amps (depending on length etc) but you would have to thoroughly check to make sure as there may be a joint somewhere where the cable size is reduced or some other issue.
By the way, funny looking main DB!?
Also quite surprised to see a bare neutral wire from the earth leakage to the ELP neutral bar
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