I have a high rise block of 80 flats with 4 flats per floor built in the 1960s.

The flats have a common ventilation system serving all the bathrooms. Galv duct from each flat into a common concrete duct that risers to a fan mounted on the roof.

The FRA has raised the question/action regarding fire dampers and cold smoke dampers, that these should be installed to each flat to prevent fire and cold smoke entering the common ventilation system and spreading to other flats.

The system is not constructed as a shunt system and some intumescent grilles have been fitted over the years to some flats where access was gained/allowed. The Fire risk assessor has stated intumescent grilles will stop hot gases and fire but not cold smoke.

Do I require motorised smoke dampers linked to a smoke detector for each flat?

You need a specialist to survey and advise you.

Is the existing common extract arrangement a significant route for smoke spread?

Can the risk be tolerated under a risk-based assessment?

Would passive measures (fire-rated terminals, intumescent devices, fire stopping, fan control changes) achieve an equivalent outcome?

Is a full retrofit of smoke/fire dampers actually required?

Risk assessors need to be grounded in reality and what is proportionate and achievable. Combined smoke and fire dampers are expensive & very intrusive to fit with a lot of disruption required as well as needing a suitable fire detection system to activate them. You then have ongoing access issues and expense for the required ongoing test & maintenance programme that would then be required.

Whilst capital retrospective works are sometimes unavoidable this is often due to legacy defects in far more modern blocks than compliant at the time of build existing older ones and should not be required lightly.
I've had a similar issue on a far larger block but the fact the grilles were mainly in low risk bathrooms was accepted by all relevant parties including enforcers as adequate - where they did pass through kitchens they were mostly found to be already filled in or plain intumescent grilles accepted. As a larger building than yours the shaft had mechanical roof extract which was deemed to assist with the issue.

In your case it sounds disproportionate based on your information.