That most often comes from font ligatures.
I see the same in the Sandbox on Windows 11. Whatever the default monospace font Obsidian is using has those. I don’t see it on macOS.
If you change Settings > Appearance → Monospace font to a different monospace font without ligatures, it should be fine. I randomly picked Source Code Pro (not sure if that’s in Windows by default) and the => weren’t combined in the code block.