Programm opens up when I start the Mac, but isn't listed as a log-in item

Try looking in the following directories :

• Items in /Library/LaunchDaemons and /System/Library/LaunchDaemons load when your Mac starts up, and run as the root user.
• Items in /Library/LaunchAgents and /System/Library/LaunchAgents load when any user logs in, and run as that user.
• Items in /Users/your-username/Library/LaunchAgents load only when that particular user logs in, and run as that user.

If you see a file there that looks sketchy, I'd move it to a temporary location and reboot.

Are you not going to tell us what app this is, perhaps it has a 'launch at startup' preference that can be switched off. Does it have a menubar icon, if so click on that and see if there is a startup option on/ off there. With the app on do you see its name at the top left of the screen, if so click on that and see if you can select Preferences, and look at the different settings you can select.

There are also other areas on your mac that an apps startup can come from it doesn't have to be in the Login Items in System Preferences> Users & Groups. For example in the /Library there is LaunchAgents and LaunchDaemons and also Startup Items. As Catalina is pretty much locked down if your find files for your app in any of these folders you will probably will not be able to delete them.

So where did you get this app from, when you click on the icon in the menubar what options do you get.

Have you ran malwarebytes on your mac, https://www.malwarebytes.com/mac/ there is a free version.

If you open Launch Agents or Launch Daemons go through the list and make a note of any that you do not recognise are from a reputable software developer. Where do you download your apps from, do not use intermediate sites as they have the potential to include malware in the download. Only download from the App Store or direct from the software vendor.

You could also download and run this diagnostic app, http://www.etrecheck.com this will generate a report with an overview of your mac and its apps which is useful in pinpointing areas of concern. The app is trusted and does not disclose any personal information. Once the report has been generated, click Share Report, this will copy it to the Clipboard on your mac, to share it on here all you need to do is open a reply

here and then click on the Additional Text icon third from the right on the row of icons at the bottom of the Reply window and paste the report in.

And if none of these remedies finds it I would urgently consider a data backup followed by a disk reformat and a clean install without automated data recovery. I would not want an unexplained "internationally based" app running in my mac.

You can tell if it is in your personally controlled domain by creating and testing a new admin account. If it is still there then it might be difficult to remove.

Sorry that was meant for OP

When you shut down the mac, there is a little popup window that asks you if you want the open apps to open automatically. if that is checked, any app you had open will launch automatically.