Attempting to import Web content as a PDF into DevonThink via the menu bar ends in blank PDFs.
I have observed this behavior only since version 3 (3.6.3) in Devonthink, both under macOS Big Sur and Catalina.
What’s the URL of the web page? A screenshot of the Sorter’s Clip to DEVONthink tab before capturing would be useful.
It happens with several web pages
I tried it with the same text (being intrigued by seeing someone else reading the same daily 
using the share icon in Safari (RTF-Text, not de-cluttered). That worked ok here.
Works fine over here. Does restarting the app or rebooting the computer fix this? By the way, you could also use the Take Rich Note service of DEVONthink and capture only the interesting part of the page (without all the navigation & ads).
For me it’s the same like for sanders011, with both Safari and Firefox. The PDF is empty. But uncluttered PDF works!
My guess is this is due to the taz paywall (which is a very friendly one, by the way)? I don’t see the paywall message in Safari (with 1Blocker) anymore like I did until a few months ago. But it is there in Firefox. And maybe for DEVONthink too.
Since all webpages behave differently when it comes to saving I use Print and Save PDF to DEVONthink 3 most of the times because than I can get a glimpse of the outcome. When printing though using the Reader Mode is recommended because it doesn’t have the ligatures bug of Apples PDF rendering. Sigh.
Yes, RTF works here too – but I would prefer PDF…!
Single page PDF or paginated PDF?
It does not matter…
Single Page or paginated doesn’t make a difference. Uncluttering does.
No, restarting doesn’t fix the problem. BTW: RTF only works decluttered…
Works with and without decluttering but PDF does indeed not work without decluttering. We’ll check this.
In your screenshot, you used RTF, though.