Not sure what box you mean. The Reply to Digest action is on the right- click menu when focused on the digest message. I'm using 3.18.5.2 and don't have any digest messages to look at.
"If you wish to reply to a component message, use your mailer's facility for this. In Evolution: right-click and select from the pop-up menu."The current text already says this. What are you proposing to change? Note that I don't have 3.20 so if there's something new I'll need to see it.
If attachments make it through the list, then take a look at the attached low quality image. On top of the image you see a MIME digest and in the upper left corner of an attached mail within the MIME digest, a box to select what to do, e.g. "Reply to All". Below this there's a plain text digest, with the menu that appears by a right click. There's no special digest option available. The version of Evolution is 3.20.1.
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