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Make sure your launcher is the latest version (you can check that by looking at the filesize, latest one is 4123KB), if it's not download it from here: https://cdn.plutonium.pw/updater/plutonium.exe.
follow this video guide https://streamable.com/5giauo.
run the launcher as admin.
if you use mcaffee, uninstall it.
Try changing your dns servers using this guide https://www.windowscentral.com/how-change-your-pcs-dns-settings-windows-10