From the dedicated website: https://nautika.evisitor.hr (the same one used in previous years) it has been possible since 2023 to pay the tourist tax online together with the "old" navigation tax.
There are two payment methods:

• By vessel length
  The payment of the tourist tax is not required for boats of less than 7 meters.
  The rate varies according to the length of the boat.
  The minimum booking period is 3 days
  
  
• By number of people
  In this case the cost depends on the number of people who are part of the crew.
  The cost is €1.33 per person per day.
  The minimum bookable period is 1 night (24 hours)

The full pricing table is shown here:
https://nautika.evisitor.hr/pricelist/

PS. in the photo the splendid bay of Punta Salvore in Istria