Hey there,
We suspect that the system still deleting the installation file which is at JoomlaFolder/tmp but you already click on that 'launch backend' button so the file can't be deleted successfully and will redirect to the installation page again.
I had removed the installation file from your JoomlaFolder/tmp already and it should be working fine now.
Can you have a try and see how it goes?
For your information, this account that you provided does not have full privilege of Super User.
https://take.ms/llB1a