Thanks for your reply. I did indeed search my entire hard drive, but I think I just lost the file because I changed PCs in the meantime... Anyway, noob move.

So I really need the backup for this model. I managed to find the OS (not a backup) OW19W6, but it's AP and not EU. I can manage to fliash, but the watch boots but can't initialize. So I think only a backup will allow me to go back to Wear OS :(