Photo Project Extensions

My Mac Mini (mid-2011) is incompatible with OS Mojave and OS High Sierra doesn't seem to be available any longer from the App Store so I still have OS X El Capitan (10.11.6). I know I can no longer design photobooks and calendars directly within Photos but I can't download the Mimeo Photos extension because it's incompatible with my operating system. Is it compatible with OS High Sierra and, if so, is there a link where I can find it and download it? Or, if Mimeo Photos is only useable with OS Mojave, are there other third party apps I can use where I can pull photos directly from my mac without uploading them to dropbox, etc? And where they can be printed and mailed within Canada?