Forced to use WhatsApp? How does that work? Whoever "forced" you to do so didn't provide you a phone?

You can probably get a local eSIM with a phone number, e.g. https://www.telekom.de/unterwegs/esim but AFAICT that's also KYC, unlike data-only eSIMs, so that might not help you much, depends on your threat model (e.g. does T-Mobile share data with Meta or not).

Look for ubigi, worldwide e-sim for fixed periods of time

there are some cheap services on kycnot.me

On what country do you live? That's a big factor

I think there are IoT sims that can only receive SMS.

My friend wanted to make something with them (I think smart thermostat) when the internet wasn't everywhere.

Same thing in the UK, except you've got to top it up at least every 3 months, minimum of £5 each time IIRC, or they disconnect it.

Personally I'd be up for paying £100 cash for a SIM that would stay connected for 5 years or so. Sadly, doesn't exist

https://www.simyo.nl/prepaid/bestellen