package libapache2-mod-php7.4 7.4.3-4ubuntu2.4 failed to install/upgrade: installed libapache2-mod-php7.4 package post-installation script subprocess returned error exit status 1

Thank you for taking the time to file a bug report.

I launched a Focal LXD container and repeated the last commands you issued to install Apache2, MariaDB and php-mysql (as seen in the DpkgHistoryLog.txt). I was able to install all three packages sequentially without any problems.

I tried to purge and reinstall packages to see if I could force any failure, to no avail. Here's what I tried:

# apt purge apache2
# apt install apache2
# apt install --reinstall libapache2-mod-php7.4

These two lines from your bug description seem to be relevant:

modified.conffile..etc.apache2.mods-available.php7.4.conf: [deleted]
modified.conffile..etc.apache2.mods-available.php7.4.load: [deleted]

I'm not sure how those files got deleted, but they shouldn't have. Can you provide more info on the exact steps you took in order to trigger this bug? Also, if you could provide a reliable reproducer for it (you can try using an LXD container for that), that would be great.

Since it seems likely to me that this is a local configuration problem,
rather than a bug in Ubuntu, I am marking this bug as 'Incomplete'.

However, if you believe that this is really a bug in Ubuntu, then we would
be grateful if you would provide a more complete description of the problem
with steps to reproduce, explain why you believe this is a bug in Ubuntu
rather than a problem specific to your system, and then change the bug
status back to "New".

For local configuration issues, you can find assistance here:
http://www.ubuntu.com/support/community

[Expired for php7.4 (Ubuntu) because there has been no activity for 60 days.]