Help Raspberry Pi Install

[david]

Folks

I have been trying to install Ubuntu 20.04.3 for Raspberry Pi 3, 
which has previously run older versions of Ubuntu and RedSleeve, and 
came across the following issues:

1)  When installing libmailtools-perl, I get the diagnostic:
   files list for package 'libmailtools-perl' is missing newline
this is not a good sign.

2)  Moments after the initial boot, it appears that the 
unattend-upgrade process starts running before I get a chance to 
prevent that function.  As a result, I need to sit and wait for 5-10 
minutes (depending upon internet speed) before I can do my own 
customization, because the updating function appears locked.  I can 
eventually get to test my own procedures, but the 10 minute interval 
is really annoying.  Is it possible, in the initial boot image, 
either not run the unattended-upgrade function, or delay its start 
for maybe 5 minutes after boot to give the human installer a 
reasonable chance to disable it.

Any advice you can give would be appreciated.

David