Below is my understanding of the capital gains tax treatment of the ISEQ 20 ETF, which is an Irish domiciled/authorised fund.
Capital gains tax at 23% is calculated on each individual disposal and should be accounted for to the Revenue in the tax period in which it arises (on a self assessment basis).
Because shares in the ISEQ 20 ETF are held in a recognised clearing system (Crest) the 8 year deemed disposal rule alluded to does not apply. Capital gains tax is calculated and payable only when there is a disposal of shares.