After latest April 2026 update to Ubuntu 24.04 LTS, thumbnails are no longer being generated

Following the April 2026 update to Ubuntu 24.04 LTS, file thumbnails stopped being generated. The issue can be resolved by relaxing a security restriction, clearing the failed thumbnail cache, and restarting the file manager.

Steps to fix it: Relax the security restriction immediate fix : Open your terminal and run: sudo sysctl -w kernel.apparmor restrict unprivileged userns=0 Clear the "failed" thumbnail cache: This forces Nautilus to retry generating thumbnails for files that previously failed: rm -rf ~/.cache/thumbnails/fail/ Restart the file manager: Close all Nautilus instances to apply the changes: nautilus -q Single Line Command: sudo sysctl -w kernel.apparmor restrict unprivileged userns=0 && rm -rf ~/.cache/thumbnails/fail/ && nautilus -q