MacBook Pro overheats and battery reach down to <1hr

Found the solution in external site, to solve the SECD and key chain issue, i needed to manually log-out, then re-log-in with my Apple Account. For some reason this requirement / routine was not included in the BigSur upgrade process.

Overheating seems related to the fact that 90% of processor activities are taken/occupied by the "SECD" Process of Apple Keychain (German: "Schlüsselbund"), more specifically Keychains activities with iCloud. I switched/discontinued all iCloud activities on all my devices, which helped, but certainly does not seem an appropriate solution, only an interims fix.