Today, on Windows (Windows 10 Pro - 22H2 2009: 19045) I installed Syncthing 1.29.3 over my previous version (that previous version being, I think, the release that immediately preceded 1.29.3). I discovered that after the installation, starting Syncthing popped up a terminal window, and that closing the window closed Syncthing. (Cf. this old forum post.) But at approximately the same time I had told Windows Terminal (which I believe is not built into Windows 10) to set itself as the default terminal. (See here.) Changing that setting - the default terminal, as set within Windows Terminal - to ‘let Windows decide’ allowed Syncthing to run without a visible terminal. I imagine that setting the option to ‘Windows Console Host’ would work too.
I add: I’m running Syncthing via Task Manager. I can share my particular configuration if necessary. (For, actually, I get the Task Manager to run a script which in turn runs Syncthing.)