Some websites even track exactly how you move your mouse and can have a pretty good guess of your age and they can track how many times you click something that doesn't do anything (apparently older people tend to zero in on buttons and click on things that aren't clickable more often. I heard this on older episodes of the Level1news on the Level1 Techs youtube channel, which I recommend listening to for tech news that might be up to a week out of date)

It's not just the data you obviously fill in yourself

and that's before considering cookies other than letting you auto login to a specific site you already logged in to before

Also, isn't Whatsapp owned by facebook now? Don't trust facebook or anything they own