As a normal user: why do I need IPv6?
As far as I know, the majority of websites (about 70%) do not support IPv6.
You need it because there aren’t enough IPv4.
If you have a mobile device with data, you’re likely already using it.
I don’t think that’s true. But of course it depends how you’re measure the majority of websites.
Most of the figures I see show 60-70% of the top 100 sites do support it. But maybe that does not reflect your usage.
Why do you need it? Maybe you don’t right now since ipv6 only sites are niche. The most tangible advantage I’ve seen is avoiding CGNAT. Gamers in particular don’t like that because it introduces latency. Services like Xbox live definitely do support ipv6 for this reason.
Depends on your ISP. If you live in a place where there aren't many IPv4 addresses available, CGNAT is the reason you're seeing a lot of Cloudflare/Akamai/Google CAPTCHAs everywhere, and IPv6 fixes that.