In Mint 19.3 XFCE, tried to install Shutter 0.94-1 (screen shot app) from Mint's repo.
Appears there were a few packages not listed in its dependsRecommends in Synaptic.
Debug - starting it in terminal gave a few missing things, though at least a couple of the pkg names mentioned were named exactly the same as in the repo.

I figured one it mentioned 1st (I think) - libgoo-canvas-perl, was the dev package - missing depends are often looking for dev versions, even if they don't say so.

I also thought I finally found & successfully installed the other few missing depends / recommends that apparently weren't listed in the Synaptic Shutter pkg. But it's still listing the missing dependencies in debug, and Shutter's Edit button is greyed out - as several web articles mention. If I hover the Edit shots button, it shows some of the missing packages relating to editing.

After installed missing depends & restarted LM, the Edit button was still grayed out.
One site, https://itsfoss.com/shutter-edit-button-disabled/ said for THIS problem in Shutter - in Mint 19 / Ubuntu 18, that the ORDER of installing the missing packages is important. I wasn't aware that is a common issue. I haven't tried that method yet - see if others had better ideas.

Regardless, AFAIK (it's late) there are no more pkgs in Mint 19 repo with names similar to ones Shutter says are (still) missing. I could install faster a better screenshot / editing app under PlayOnLinux than this.

Question is, now that it's installed, what's the best way to find exact names of still missing depends / recommends? Or is it easier to D/L the package & run commands on that to see missing depends? If Shutter doesn't list all depends, the latter won't help.

I believe shutter uses a perl script to launch - least an older Shutter version.
The desktop launcher uses only "shutter %F" and if I cd to /usr/bin, then cmd "shutter" does launch it. But if I'm trying to get data about the installation, like "ldd -d (or -v) shutter," then it doesn't start, stating "not a dynamic executable."

In that case, if I use "ldd -v perl /usr/bin/shutter, it starts & gives data on files installed. I don't know if any of these commands will give good info (names, locations) of missing depends, for installed apps.

The order of installing packages is important if you don't use a package management system that resolves dependencies.

The instructions you refer to do that: They ask you to download three package files that depend on each other. dpkg or gdebi will fail when you install a package whose dependencies are not already installed. Perhaps it would be possible to install all three at the same time, e,g.

but I would have to look up the dpkg man page to confirm this.

It can.

If Ralph depends on Herman, Helen, Herbert; and Herbert depends on Alvin and Amy; you have to install Alvin and Amy before you install Herbert.

If Herman, Helen, Herbert are not related, it shouldn't matter in which order you install them, but they all must be installed before you install Ralph.