I see nothing in Ubuntu/Debian (no reference I used in my earlier comment) so as I suggest you provide details as to what you are trying to install, and why you need it.
My guess is it’s something old, python2 is EOL but you’ve provided no details. I would suggest looking for a more recent version (and avoid python2 if security matters to you)
I see the Debian and Ubuntu searches you provided turned up nothing for libicui18n.so.60 or libicui18n or libicui, but I did find something here https://pkgs.org/search/?q=libicui18n.so.60.
I just don’t know how to proceed.
I am running some custom software that is kicking up an error:
error while loading shared libraries: libicui18n.so.60: cannot open shared object file: No such file or directory
I know it works fine in Ubuntu 20.
It’s just missing in Lubuntu 20.
I just wanted to see if I could run the software on an old Centrino laptop.
Maybe standard Ubuntu will work on the Centrino?
Lubuntu and Ubuntu share the same package repositories. You mention Ubuntu 20 and Lubuntu 20 but there are 2 different versions of both. Releases are in YYMM so for 2020 there is 20.04 (released in April and is a LTS release) and 20.10 (released in October).
Is a binary that is built from a package, since it is inside it is sometimes difficult to search for. Enter apt-file You can see the output below from my search on my Lubuntu 20.10 machine.