HI Ltony.1,
This is a well know issue already discussed on ST Community, for now all you need is to execute the following command in a Terminal:
xattr -c /Applications/STM32CubeIDE.app
Then you may have to unlock STM32CubeIDE from Gatekeeper too.
Note also that STM32CubeIDE does not officially support Big Sur, you might run into sporadic troubles. Anyway some user already tried this MacOS version and didn't reported major issues.
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