Bigger thumbnail size, please!

The maximal thumbnail size is 256px. I need more: 512px. I have big screens.

Preferences / Miscellaneous / Advanced: max_thumbnail_size.

In Opus 12, max_thumbnail_size automatically scales with the system DPI, so you would not normally need to adjust it, unless you wanted enormous thumbnails. Note that the larger it is, the more memory and disk space thumbnails use.