We have a wish like that: 397172 – Export size during export , I will add it to my post here Beginner coding tasks in Krita: easy and short feature requests, ready to implement - #10 by hellozee so maybe someone will pick it up.
Also since no one noticed it before now, it won’t be in 4.3.0 because now we’re in second beta testing stage, which means that only regressions (new bugs) or crashes can be fixed. It’s for safety. All other things need to wait until 4.3.1 
But somewhere around two weeks from now you’ll be able to download Krita Plus version from the website with this fix. (It’s best if you subscribe to it on the bug tracker so you know when it’s added to that version, then you need to wait 1 day so it for sure is on the version on the website, not only in the code).