Hi - that looks likely to be related to the ongoing work to improve the underlying code for overlay icons in Dolphin. The links below give some context:
- Bug report related to some of the recent changes: 499644 – Dolphin 24.12.2: Symlink folder icons/previews are too small
- Relevant merge request: Port from KIconLoader::drawOverlays to KIconUtils::addOverlays (!804) · Merge requests · System / Dolphin · GitLab
- Another merge request notes some deterioration when zooming, which may be what you’re experiencing: Refactor Overlay Handling (!889) · Merge requests · System / Dolphin · GitLab
Ultimately I don’t see an existing bug report for that specific situation, so it may be helpful to submit that (Get Involved/Issue Reporting - KDE Community Wiki) and note within that there’s a likely connection to the work above.