When I shared an album with clients, is there a way to share full resolution AND web size photos?

For basic access (when you set 'Anyone Can view', or invite specific people with Can View rights), and when people view those shared albums in via web browser, I think Melissa is right that there's no better solution.

One workaround that could be less than ideal for you: 

Invite specific people via email addresses to join your album with Can Edit rights.  

I believe this gives access to the full size image (if you have uploaded original images, and not just Smart Previews from Lightroom Classic).  People you give Can Edit access can edit and export images at the original resolution as long as the original image exists in cloud storage.

I do think there's a running thread in the Ideas channel for Lightroom here to enable full res download for basic guest viewers as well.  As always, product mgmt reviews such feedback and weighs it against new features and important fixes.

You could share a second album with the smaller files. No simple solution I'm aware of. 

it's just really silly there isn't some way to let the user choose which size they want to download. Hopefully I'm just missing some obvious option in the album...