LGPL only stipulates that users have the freedom to link against their own version of the LGPL library you're using. You don't have to open source anything if you don't want to.
> QT needs a commercial license which is pretty expensive
Are you sure about that? Most of Qt for desktop is licensed under LGPL or similarly permissive licenses that don't require you to open source your project or pay licensing fees.
Some specialized components in Qt are GPL/commercial, but those are for things like automotive use.
I use Qt/QML for desktop applications and never had to buy a license.
Check this out[1] and sort by license to see if you're actually using modules that require a commercial license. Chances are you aren't.
A while ago, I found the need to stream directly from yt-dlp instead of downloading full videos[1]. You can have yt-dlp write to stdout and pipe that stream into your player of choice.