It's an extremely annoying process, but here is a video I whipped up demonstrating how to combine two or more scenes into one timeline. It becomes considerably more time consuming as the number of scenes you wish to merge increases, since there is a lot of prepwork to get each scene "ready" for being merged, in addition to having to fix bone colliders and such. I am also a dumbass, so there might be an easier way to do all of this that I am just not aware of. This is just how I figured out how to do it from dissecting how scenes are created.
I unfortunately can't post it on a stream-friendly platform, so here is a mega link for a direct download:
https://mega.nz/file/5WBAHT7K#ow1pvPQqRv_6q5967psGciWmPOIDkAfkRzamLD0ji9g The most difficult to explain part was setting up the folders of each animation so they enable/disable at the right times. I wasn't quite sure how to articulate this as the language becomes quite repetitive, but if the process in the video is confusing for you or anyone else I will see if I can find a better way to word it, or make an easier to follow method of demonstrating how it's done.
Scenes which are animated relying on nodeconstraints CAN be merged like this, too, it is just a lot more annoying since if you have to tweak anything with nodeconstraints...well, you'll have a massive list of constraints to go through before you find the ones you might need to edit. This can be mitigated ahead of time by renaming all of the nodeconstraints used for each individual scene to something easy, like adding a "SCENE01" prefix to each constraint's alias, prior to importing it into another scene for merging.