All coins coming from the year 2022 or earlier have an image of Queen Elizabeth II on the reverse of the coin. This changed after the death of the queen in September 2022.
Something special is going on with the coins from the year 2023. The first 2023 coins were struck with an image of Queen Elizabeth on the reverse. Then The Royal Mint chose to mint the rest of the 2023 coins with an image of King Charles III on the back. This means that there are gold Britannia 2023 coins with both Queen Elizabeth II and King Charles III depicted on the reverse of the coin. The Royal Mint was the only mint to issue investment coins with an image of King Charles III as early as 2023.
As of 2024, all newly minted gold Britannia coins contain an image of King Charles III.