Hi @nebunie Gabriel :)
My reco is to uninstall , then fresh install the new Bitdefender Antivirus Free.
Stay safe,
Mike
I ran into same issue by upgrading bitdefender free too
here is my solution
launch "disable early-launch anti-malware protection" in safe mode menu
you should be able to boot into windows and reinstall bitdefender free
I'd be careful with the above if you have Bitlocker enabled, you may end up booting into Windows Recovery, Repair, etc mode. You could run into a headache unless you have your recovery key printed off, just in case.