I have the same problem, but I found a three ways around it. 1) press the three dots on the top right, go to downloads then tap on the file, then press install, wait for it to download, then press open when the install is complete. 2) do the same thing in brave, though the three dots are on the bottom right. 3) if all else fails install either https://play.google.com/store/apps/details?id=apk.installer.apkinstaller or https://play.google.com/store/apps/details?id=com.apkmirror.helper.prod