Yes and no? It's not quite as black and white as that though. Yes, they can technically decrypt anything that's been encrypted with a cert that they've issued. But they can't see through any additional encryption layers applied to that traffic (eg. encrypted password vault blobs) or see any traffic on your LAN that's not specifically passing through the tunnel to or from the outside.
Cloudflare is a massive CDN provider, trusted to do exactly this sort of thing with the private data of equally massive companies, and they're compliant with GDPR and other such regulations. Ultimately, the likelihood that they give the slightest jot about what passes through your tunnel as an individual user is minute, but whether you're comfortable with them handling your data is something only you can decide.
There's a decent question and answer about the same thing here: https://community.cloudflare.com/t/what-data-does-cloudflare-actually-see/28660
We all need to decide for ourselves what we're comfortable with and what we're not and then implement appropriate measures to suit. I'm not sure why you're arguing with me over how I setup my own services for my own use.