$ sudo apt-get install php7.4-imap
php7.4-imap : depends on: php7.4-common (= 7.4.3-4ubuntu2.5) but7.4.15-7+ubuntu18.04.1+deb.sury.org+1 should be installed
$ sudo apt-get install php7.4-common
php7.4-common is up to date (7.4.15-7+ubuntu18.04.1+deb.sury.org+1).
（大致翻译了apt答复）
我在其他帖子中发现了类似的问题，因此从中删除了一些过时的存储库/etc/apt/sources.list.d；结果没有变化。有什么想法吗？
sources.list已于二月修改（可能在更新中）；xenial被替换为focal。这可能是问题所在吗？如果是：我该如何解决？
sources.list：
# deb cdrom:[Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5)]/ quantal main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu/ focal main restricted
deb-src http://archive.ubuntu.com/ubuntu/ focal main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted
deb-src http://archive.ubuntu.com/ubuntu/ focal-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu/ focal universe
deb-src http://archive.ubuntu.com/ubuntu/ focal universe
deb http://archive.ubuntu.com/ubuntu/ focal-updates universe
deb-src http://archive.ubuntu.com/ubuntu/ focal-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://archive.ubuntu.com/ubuntu/ focal multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-updates multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-security main restricted
deb-src http://archive.ubuntu.com/ubuntu/ focal-security main restricted
deb http://archive.ubuntu.com/ubuntu/ focal-security universe
deb-src http://archive.ubuntu.com/ubuntu/ focal-security universe
deb http://archive.ubuntu.com/ubuntu/ focal-security multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu quantal partner
# deb-src http://archive.canonical.com/ubuntu quantal partner
deb http://archive.canonical.com/ubuntu focal partner
deb-src http://archive.canonical.com/ubuntu focal partner
更新：我删除了所有 php7.4 软件包并重新安装它们（加上 php7.4-imap）。这导致降级到 php7.4-3，但至少它可以正常工作。