Here is what happened: after receiving the Mission 22 debriefing, the power cut out during the loading screen that appears before the aircraft selection menu.

Please implement a system for additional backup saves, at least for the campaign. As the title explains, I lost my progress due to a power outage; when I launched the game, it prompted me to create new data, but this synced with Steam and I couldn't recover my save from the cloud. Just as the game creates replay files, it could also create multiple backup save files to prevent this issue.

For now, and for those reading this, I would recommend performing a manual backup.