In principle, the alcohol content in cosmetic products does not have to be explicitly stated, as is the case for beverages, for example. There is also no maximum use concentration (corresponding regulations would be found in Annex III of the Cosmetics Regulation).
Although liquid food supplements are not considered beverages, it can nevertheless be assumed that, in accordance with the Food Information Regulation (LMIV), the alcohol content must be indicated in % by volume. Corresponding judicial decisions suggest this.
From the Food Information Regulation (LMIV) Regulation (EU) No. 1169/2011
The actual alcoholic strength by volume of beverages other than those referred to in paragraph 1 containing more than 1.2% alcohol by volume shall be indicated in accordance with Annex XII