Just don't give your cell number to people. I use a virtual number for almost everything.

"I don't have a mobile phone and the law doesn't require me to have one"

Or have 1 cell phone line that you give out as your number, set it up with an app to auto-forward SMS to an e-mail address and calls your actual cell phone, and put that phone in a locked garage in the middle of Iowa.

A lot of sites have started requiring a non VOIP phone number. Have you noticed this uptick? I used to use my google voice number for everything but it gets rejected as "not a real number" about 2-3x a week

Try using a non-US number. Many of them aren't good at differentiating VOIP/non-VOIP numbers in places other than the US.

I don't use any services that validate phone numbers in any way. Why would I?

Whenever a website asks me for a phone number I just make up random digits. Have never run into problems. Credit card companies definitely don't care what phone number I give to merchants.

I had to validate a phone number just to order food at MULTIPLE restaurants in the bay area using the ordering interface at the QR code at the table. They did not have paper menus. An SMS confirmation was required just to place an order from sitting at the table. This wasn't even for payment, just for ordering.

The DMV also required a stupid SMS confirmation just to renew my car registration.

I use virtual numbers for pretty much everything, but yeah, welcome to 2023.

The SaaS I've been encountering requires reporting a text received by the number to confirm the account.