It's seems to be solved in the subsequent release 7810:
Build 7810 (May 20, 2021)
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- Fixed: Special and accented characters might be improperly encoded in calendar appointments and invitations.
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Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)