Adelmo83 Thanks for your input! Spinebot's answer is correct, but we are actually aware that there should be another way to easily reverse the order of the keys, since the box selection method does not work in some cases, such as keys on fractional frames. Here is an issue ticket for this improvement, and I have added a link to this thread as a comment:
EsotericSoftware/spine-editor819
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To paste keyframes in reverse in Spine, you can manually achieve this by copying the keyframes you want to reverse, moving them to the right, and then dragging a selection box around them. Once selected, drag the left side of the box to the right side to invert the order of the keyframes. This effectively reverses the animation. While there isn't a direct "paste in reverse" feature, this method allows you to reverse keyframes manually.

The features you are requesting, such as global offset, motion trails, bookmarks, and animation layers, are not currently available in Spine as you described them. However, there are some related discussions and feature requests that have been noted by the Spine team. For example, there is a request for a non-destructive offset for secondary motion, which might relate to your global offset need. You can find more about this in the GitHub issue here. Motion trails have also been requested, and you can follow the discussion here. As for bookmarks, there is an idea to add timeline markers, which you can see here. Lastly, while animation layers are not directly supported, there are plans to improve the Preview view to allow for more complex animation editing, which might offer similar functionality in the future. You can follow the progress on this feature here.

Adelmo83 Thanks for your feedback! As for the window that allows saving the selection of the bones, we actually have a similar idea in our roadmap: EsotericSoftware/spine-editor409

As for drawing tools, we are basically not considering them. We agree that it would be beneficial, but there are many things to improve when creating animations, and we would prefer to focus on those.

By the way, as a somewhat interesting example, one user mentioned that he uses path attachments to illustrate feedback. This is not a very good solution, but I thought it might be useful to some extent when asking someone to change the trajectory of movement, since adding a path attachment for feedback does not affect the final exported skeleton data at all, as long as the Export checkbox is unchecked in the properties.

The idea of having a window to save bone selections in Spine is a useful suggestion that could enhance animation workflow efficiency. Currently, you can store selections using Ctrl+0-9 and retrieve them with 0-9, which might help in managing selections. As for a basic drawing tool, there have been discussions about adding simple sketching capabilities in Spine, similar to a grease pen, for making pose adjustments or providing feedback. However, Spine's focus remains on its core strengths in skeletal animation, and it may not compete directly with dedicated drawing tools like Photoshop.

Hello,
While it will likely not be possible to make such an improvement for an older version of Spine, I have verified that also 4.2 json export doesn't include stored selection, and indeed it would be a useful feature. I have opened an issue to track this proposal:
EsotericSoftware/spine-editor848