This is my workflow:

1) I browse files in LRTimelapse, and wait for it to build previews.
2) I drag files to Lightroom Classic 12.1 (making sure Add option is selected). There I apply my color grading, sync all the files.
3) I go back to LRTimelapse, click visual previews, but i keep seeing default images, no changes I made in Lightroom are apparent.

Log file included.

And did you write back the metadata to all files?

In Lightroom, after editing your keyframes, you need to go to Library Mode (Grid View - hit key "G") and then Metadata / Save Metadata to Files). If you do if from Develop Module it won't work.
After that, LRTimelapse will automatically pick up the changes on the keyframes and start developing them.

If this doesn't work, please check this faq with step-by-step troubleshooting:
https://forum.lrtimelapse.com/Thread-key...vise-versa

Yes, that did it. Thank you guys.