Undo/Redo is on our roadmap but it's a fairly large feature (which is why we haven't built it quite yet). We're hoping to release v1.1 in the next week or so, which adds a lot of Quality of Life updates but does not add Undo/Redo. We're currently planning to ship Undo/Redo in v1.2 which is likely to release in mid to late February based on our current velocity.
TMX export is in our overall backlog but not committed to a specific version just yet. Exporting tile layers to TMX should be fairly achievable. However, TMX doesn't (as far as I know) support arbitrary item placement. So that's something that will require more investigation before we commit to that feature.
Thanks for using the tool, and your feedback!