• Go to https://j-novel.club/series.
• Enable A-Z sorting in the filter.
• Advance the search results until you see titles that start with D.
• Observe that DUNGEON DIVE: Aim for the Deepest Level appears in the list before Dagashi-ya Yahagi: Setting Up a Sweets Shop in Another World.

My assumption is that each character is being compared by codepoint value, which is why the capital U in DUNGEON is considered alphabetically earlier than the lowercase a in Dagashi as capital letters have a lower codepoint than lowercase letters.

This can be seen with other series that start with multiple capital letters, such as RVing My Way into Exile with My Beloved Cat: This Villainess Is Trippin' which appears before Re:RE — Reincarnator Executioner in the results.