Thanks for your input Lukas. Your points are valid, and others share your concerns with the replacement of enigmail by a built-in implementation that doesn't use the system keyring.
Unfortunately thunderbird 68 won't be supported with security updates for much longer, definitely not for the remaining lifespan of Ubuntu 18.04 and 20.04. So the upgrade to 78 isn't avoidable.
Thanks for your input Lukas. Your points are valid, and others share your concerns with the replacement of enigmail by a built-in implementation that doesn't use the system keyring.
Unfortunately thunderbird 68 won't be supported with security updates for much longer, definitely not for the remaining lifespan of Ubuntu 18.04 and 20.04. So the upgrade to 78 isn't avoidable.