Can I just use 1.0.0.1?

ISP hijacks 1.1.1.1 and won’t fix. Is it ok to use 1.0.0.1? Or best not to use CF in such a case where 1.1.1.1 is hijacked/blocked?

That’s (1.0.0.1) the preferred solution in your situation.

Interesting.
Have you already contacted them about this issue?

How about 1.1.1.2 or 1.1.1.3 instead of 1.1.1.1 (regarding the known differences due to content serving & protection)?
Or it has to strictly go “in pair” like 1.1.1.1/1.0.0.1, 1.1.1.2/1.0.0.2 and/or 1.1.1.3/1.0.0.3?

I just wonder, what happens if you use a VPN like ProtonVPN (I am not their reseller, rather user on demand) with custom DNS servers like 1.1.1.1 and 1.0.0.1 - which works for me (if that can help in this issue or your case)?