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You could try enabling Screenshots in settings, found under General, and then view the screenshot and zoom into it on the Photos app.
 
Mail on my watch is pretty much unusable - not because of text, but because it takes absolutely ages to refresh with new mail.
 
The workaround:

Use Outlook for mail on your iPhone/Watch.

Email is MUCH more legible, and I think it's absurd that Apple hasn't addressed this.

My Mail complication is now Outlook, and I'm getting notifications from Outlook, instead of mail, on my iPhone/Apple Watch.
 
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