I’ll definitely keep an eye out on this club, despite binging the first volume already. Just couldn’t stop reading.
This is unfortunately the same everywhere else in my experience. The digital version has been compressed with a lossy algorithm at least a couple of times (although probably not actually scanned). I did a bit of investigation in Absolute Beginners Book Club // Now reading: Horimiya // Reading Next: Miss Shikimori is not just cute! - #1891 by eagleflo but I never found the slightly better version for sale digitally – it’s just the publisher preview.
If I knew Japanese I’d write to BookWalker or the publisher and ask them for a revised edition – they do have clean masters, otherwise this wouldn’t get reprints.