It seems like the happy ending is just merging with the rest of society rather than sticking to your own identity. Being true to yourself isolates you from everyone else, makes everything feel cold and distant. It's a constant battle to stay alive and caring in such a cold existence, but it's the only way to be yourself and not what others want you to be.
You could extrapolate that to AI- how most of society now relies on it, has integrated with it, despite it being a facade, a crutch designed to deprive people of knowledge and skill. The tapes could represent how AI is corrupting the past, taking IPs and happy memories and distorting them until they're unrecognizable. About the allure AI has when everyone you know and love is enthralled with it, like with the piano scene at the end. It takes beautiful melodies and plays them perfectly, indistinctly, without a humans touch at all, and as generically as possible.
There are parts of this game that hint at Lera being a trans woman, though, which leads to a different interpretation of the game. Her tomboyish style, her experiencing social rejection from others that view her as "gross", her hating her own reflection, etc would make sense when combined with the theme. Or maybe it's related to her nostalgia for the USSR and the economic prosperity it brought, considering how all of the rooms are covered in propaganda posters of the time and her desire to build massive, brutalist, utopian megastructures common to the time. Even the offhand comment to the little girl that she couldn't be a cosmonaut because "space isn't profitable."
It could also just be about nostalgia as a concept, how it can feel like a warm retreat from everyday life and suck you in and make you want to bask in it forever, but you can't live in the past. You have to return to the present at some point, no matter how cold and lonely and depressing that present is.
All of these themes could be present in the story, whichever one resonates with you most is what you can assume it's about. All stories are about what we decide them to be about, after all, and that's dictated by the emotions we feel while playing it, not "logically decoding" the "real" meaning the author "intended" for people to take away from it.