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
MMS yes, by deleting all the APN profiles. Always did it since 20 years ago
Can disable SMS sending by changing the "SMS center number" but I don't think can disable reception
Luckily in my country the carrier in the early 2000s they decided to scam users with MMS and the "internet button" nearby the "OK" button and not with the "SMS double dip" where both sender and receiver would be charged for texts - too prone to abuse from assholes with large plans
"Internet button scam" explained for young people: in the early 2000s some carriers charged 1-2 euro each time you started an internet session. This for two main reasons:
To block new chat apps. We had "jar" apps like ebuddy, IMO or jacksms that could let the user chat spending much less. They were super optimized for data saving and even at the astronomical 20 euro per MB that they were charging at the time, it meant a chat session with a friend would cost 8 cents instead of 3 euro of texts. I would make two short calls to my friend, it would mean "go online and check the chat"
Get free money from people with fat fingers. Opening the browser would immediately charge the user 2 euro. There was a competition between phone makers to place the "internet button" in the most asshole position. Nearby the "call" button, or as a dynamic button, like at the home screen, the "ok" button would open the internet, while in the menu would be "ok". I had a Motorola where they placed it in the middle or the D-pad and I always accidentally pressed it. This could be mitigated by avoiding the purchase of a "carrier branded" phone because it could be toggled off. If you bought a phone with Vodafone branding instead every button had a way to let you spend money