Solved
The update site for STMCUBEIDE http://sw-center.st.com/stm32cubeide/updatesite1 doesn't resolve and throws a 404 error. Any ideas guys?
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If you are behind a proxy make sure that your settings are correctly set, the reload button may help to validate them.
Otherwise I suggest you to clear your p2 cache by deleting the following folder, and try again Help > Check for updates:
INSTALL_LOCATION\STM32CubeIDE\p2\org.eclipse.equinox.p2.repository\cache
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