I looked a little more into apps that supports UPnP/DLNA and Chromecast and found the following. Again, not being a programmer or developer, I don't know if this is helpful or not.
Updated Recommendation (Based on What’s Currently Possible)
Given the tools that do exist (or are actively maintained), here’s what I’d lean toward now:
• Use Neutron on Windows for your primary playback: for its audio quality + casting flexibility + LRC lyric support.
• If you want to see synced lyrics on your TV / Chromecast, still use a secondary / mirrored approach: run a lyrics-display app or lyric viewer on your PC (or browser) and mirror that to the Chromecast.
• Use BubbleUPnP Server (or similar) if needed to make your network architecture more flexible (especially for DLNA casting).

Open-Source / GitHub Projects to Watch
Here are some open-source projects (or libraries) that are relevant, plus their gaps / potential:
QuickBeat A more fully-featured Windows music player. From its GitHub: supports UPnP/DLNA servers + renderers, plus LRC / synced lyrics. GitHub
This is probably the closest: native Windows app, casting support, and lyric sync. But it's still under development / not super mature.
QuickBeat seems most promising for your use case. It supports UPnP/DLNA and LRC-synced lyrics per its feature list. GitHub If you’re okay using an app that’s still in active development / somewhat niche, this might be the best bet.
I looked a little more into apps that supports UPnP/DLNA and Chromecast and found the following. Again, not being a programmer or developer, I don't know if this is helpful or not.
Updated Recommendation (Based on What’s Currently Possible)
Given the tools that do exist (or are actively maintained), here’s what I’d lean toward now:
• Use Neutron on Windows for your primary playback: for its audio quality + casting flexibility + LRC lyric support.
• If you want to see synced lyrics on your TV / Chromecast, still use a secondary / mirrored approach: run a lyrics-display app or lyric viewer on your PC (or browser) and mirror that to the Chromecast.
• Use BubbleUPnP Server (or similar) if needed to make your network architecture more flexible (especially for DLNA casting).
🔍 Open-Source / GitHub Projects to Watch
Here are some open-source projects (or libraries) that are relevant, plus their gaps / potential:
QuickBeat A more fully-featured Windows music player. From its GitHub: supports UPnP/DLNA servers + renderers, plus LRC / synced lyrics. GitHub
This is probably the closest: native Windows app, casting support, and lyric sync. But it's still under development / not super mature.
QuickBeat seems most promising for your use case. It supports UPnP/DLNA and LRC-synced lyrics per its feature list. GitHub If you’re okay using an app that’s still in active development / somewhat niche, this might be the best bet.