If you already have a Ukrainian COVID certificate in the Diia app, this will be valid in all countries throughout the EU.
If you do not yet have a COVID certificate, you can get one by getting vaccinated against COVID-19 in Sweden. You can get a COVID certificate after the first dose of the vaccine, but most countries require you to have had at least two doses in order for you to enter.
It is important that you find out the rules that apply in your destination country.
Do you not have a Swedish personal identity number or coordination number?
If you have been vaccinated in Stockholm, you can call +46 8 123 365 78. There you will get help to obtain a COVID certificate, which will be issued by the Swedish eHealth Agency.