Note for Americans: here WhatsApp is the de facto communication standard. Literally nobody uses SMS/iMessage/Facebook messenger/signal. And carriers still charge 2 euro for a MMS which completely kills iMessage/RCS (if accidentally send MMS, it's expensive)
I switched phones and instead of copying manually /Android/data/media/com.whatsapp I used the new feature of pairing via qr code.
Besides that's a not very well designed feature (you need to start transfer on the old phone before logging in the new phone) because they really want to store unencrypted backups on Google drive, the transfer completed in a short time.
Maybe too fast, I was expecting at least one hour to transfer the 5000 photos 10gb, instead it completed in 20 seconds.
So I told myself, ok photos not transferred, I'll just do that manually and directly put them in the photo archive on my PC rather than keep them mixed with all the "happy holidays" trash.
I browse the old phone to /Android/data/media/com.whatsapp and... It's empty. Wiped clean after the "successful" transfer process!
Luckily I had set syncthing (the fork on fdroid, the one on play store doesn't have access to whole storage) to have a full overnight backup! On my PC I still had all the photos, almost deleted too as I noticed that I didn't set the "trash can" option
Conclusion: go to download syncthing fork from fdroid and have a safety net from mistakes like this
schedule that works only when charging and only at my home wifi (native setting of syncthing fork)