I am not a Croatian citizen

If you do not have a Croatian electronic ID but are a national of a European Economic Area (EEA) member state, you can identify yourself using the credentials from your national electronic ID and sign the documents using your qualified electronic signature issued by an EU trust service provider from the following list https://webgate.ec.europa.eu/tl-browser/#/.

Each founder of a company must have a Croatian Personal Identification Number (OIB) issued by the Ministry of Finance, Tax Administration. If you do not have a Croatian OIB but you are a national of an EEA member state, you will be redirected to the Tax Administration website to apply for an OIB. Once you have received your OIB, you can proceed with the establishment of a company.