https://www.denik.cz/z_domova/britanie-volby-cesti-politici-20191213.html
Username: @honzakolarik
The czech news page https://www.denik.cz/ hides all article content from the user and shows a popup to disable any AdBlocking software. The page works normally if the user disables AdGuard or disables JavaScript in the browser. Please let me know if you can resolve the issue or if you only deal with english language websites.
Screenshot 1

Information | value
--- | ---
Platform: | Win
AdGuard version: | 7.2.2990
Browser: | Chrome
AdGuard driver: | WFP
Filters: | Ad Blocking:
AdGuard Base
Social Widgets:
AdGuard Social Media
Annoyances:
AdGuard Annoyances
Language-specific:
EasyList Czech and Slovak
Not reproduced with Czech VPN, please check @zloyden @AdamWr
Unfortunately I can't reproduce it too.
Screenshot

I can, with AG for Windows only. This is caused by element hiding, but cannot find which rule causes it.
Maybe:
denik.cz#$#.reklama-box[id] { display: block!important; }
Hm. Earlier tried $generichide and disabling domain specific rules, and detection was shown.
But now I don't see it. Probably app has some delay.
Works fine with
denik.cz#$#.reklama-box { position: absolute!important; left: -3000px!important; }
denik.cz#@#div[class^="reklama-box"]
denik.cz#@#div[class^="reklama"]
denik.cz##.reklama-box-leaderboard
I might be wrong, but it seems that adblock detection is from https://www.googletagmanager.com/gtm.js?id=GTM-TGXTRC and looks like that:
adbCheck(){var a=document.getElementById("QYBnxWEArcyG");return 0==a.clientHeight?!0:!1}
Screenshot

Yep. This filter was disabled.
Added to Annoyances.
Most helpful comment
Added to Annoyances.