For some products there may be a requirement to declare the exact % of certain ingredients on the pack for the finished product - this is an unavoidable element of regulation here, but whether it applies in your case will depend on the specific circumstances. This is detailed in Article 22 of Regulation (EU) 1169/2011.
Are your products finished goods or raw materials? For the latter you've also got the extra challenge of your customers' customers' requirements, which may expand the obligations under the same regulation.
Aside from all of that, to an extent this comes down to a decision of how much you want to do business with these people - if this is their own requirement rather than a regulatory one then you can choose to ignore it, but equally they can choose to give their money to someone else instead
Also note that for some of them this may be mandatory information for their customers, so their choice is to have the data or to not be able to sell to some clients.
As a possible compromise you may want to discuss the idea of ingredient "banding" with them - it's something I see relatively frequently in the UK. Rather than giving the ingredient list as e.g. 15.9% ingredient A, 2.7% ingredient B etc you'd detail within bands of certain percentages, so you might say e.g. 10-20% ingredient A, 1-5% ingredient B etc instead. That way your exact formulation remains confidential, but your customer gets some information on rough proportions of ingredients.