That depends on the email client settings... Some recipients might have the loading of images turned off by default. Or it can be turned off for external senders, or any other content policy might be in place...
You can add a note below the QR code like "If you can't see the QR code above, make sure loading of images in your email client is enabled."
QR Codes are embedded in the emails. They are part of the message, something like a hidden attachment. They are not loaded via a link from a remote location.
Option B would be to use AnyMerge Docs together with AnyMerge Mail. First, generate PDFs with QR codes with AnyMerge Docs. Here you just need to ensure the links to the generated PDFs are stored in the spreadsheet (for example, column F).
And then configure the AnyMerge Mail to attach the docs from column F as attachments.
Something similar is shown here: