In my case it was Microsoft Defender Antivirus in Windows 11 which has flagged the latest Stella 6.7.1 version as "potentially unwanted app" because it supposedly detected the 'PUAMiner:Win32/RedbyrepMiner' virus. It must have been be a preconceived plan by the Stella team to spread this bitcoin-miner software to all our machines, make loads of money and then take over the world! I should have known, as Stella is just too good to give away for free...
As a workaround, I installed Stella 6.7, which isn't blocked by Microsoft Defender!