You might be misunderstanding the value-add of a CDN to self-hosting, so here's my attempt at explaining:
I've been self-hosting things for a very long time. In the old days, we would wrangle our routers to expose port 80 for HTTP (and later, port 443 for HTTPS) and forward those connections to the self-host server and then add the appropriate DNS records to point our website domain to our home IP address (which was its own fun challenge when ISPs refused to give static IP addresses for home plans). Relatively simple.
However, in recent years (especially after the pandemic) the internet has become a much more hostile place. People find vulnerabilities in your nginx/caddy/apache or whatever reverse proxy you use (or router, or any one of the many other parts of your network/software stack) gain access to your local network and your personal data. And then there are bad actors doing DDoS attacks or AI crawlers generating DDoS levels of incoming requests to overload your hardware.
All that combined means it's very dangerous to have your home IP exposed to the internet (allowing any sort of inbound requests) at all.
So, how do we access our self-hosted stuff while we're outside of home? The safest approach is to use a VPN. Tailscale is the most popular one that I've come across. Only client devices that are connected to the VPN have access to your stuff. Random bad actors can't poke your self-hosted stack for vulnerabilities.
Okay, what if you want to share something with people publicly? I for one, use Immich for my photo libraries and it's very easy to be able to share a link to an album for friends and extended family to access without having to install and configure a VPN on their phones.
That is where cloudflare comes in. We can run cloudflared on our machine, which makes an outbound request to cloudflare and creates a tunnel to route all the incoming requests from their servers to your reverse proxy. Your network is still not exposed to the internet, and the edge nodes (the machines that actually front the incoming traffic from the clients) are not owned by you.
Now, I guess it's feasible to rent a VPS on DigitalOcean/OVH/Azure/AWS and run a Tailscale exit node there to achieve a similar result. I haven't looked too deeply into Pangolin but it looks kind of similar. Now you're adding extra work to keep those configured correctly (and up-to-date), is less secure because you're not doing that full time (unlike the engineers at cloudflare) and you're still dependent on that VPS provider to not go down, so the disaster recovery profile hasn't changed all that much.
That's why there's no self-hosted alternatives to a CDN. I guess you can go with their competitors like Fastly/Akamai/etc, but all of them are considerably more expensive. And even the ones that do have free tiers have data limits or bill per gigabyte. That's an extra headache to worry about for that one month your mother decides to take 1000 videos of your son during the family vacation and her phone automatically backed up all of them at full-quality.
That's news to me lol. I've personally only used them for development so I can't tell you how good they are for running production services.
I just looked at their pricing page and it looks like the Free and Hobbyist only include 1GB and 5GB of data, respectively. I've never actually measured my data usage because Cloudflare gives unlimited data, but I suspect that's nowhere near enough for a photo sharing app like Immich.