Part of the mystery why is they modified Docker’s default DNS and used cloudflare and it doesn’t play well with some router setups and in that case, you will have to change it.
After I swapped ram off a machine I wanted to run public pool and umbrel bitcoin, I ran into the same slow issues and discovered they changed the default structure of docker when troubleshooting a different problem.
I posted the solution here: Bitcoin core or knots is unusabel on umbrel and Raspberry Pi - #15 by oconical