Using the Google Chrome browser, a user will attempt to open a link they have saved in a form. In some cases the URL they fetch is not configured to be open in a new tab for the Google Chrome browser, and instead will try to force the user to download the document instead of opening it.
Google Chrome, and possibly Chromium based browsers, are configured in a specific way to search for certain strings to decide what to do with a link when selected. If it is missing the proper string to open the link as a new page then it will by default, attempt to download it as a document.
Click on a link inside of a view or form with open the Save As window to begin the download, instead of opening the document in a new tab.
Look at the URL and check to see if the "?web=1" string is attached to the end of the URL. If it is absent, append the string to the end of the URL and test it by attempting to open it in another tab.
More information can be found in this link: https://docs.microsoft.com/en-us/sharepoint/troubleshoot/lists-and-libraries/files-downloaded-instea....