Actually you need to run Tor as a router, only then you'll never leak a DNS info, but there's also a trick with persistent cookies: if you've visited some sites from your PC before going through Tor or logged into your impersonated profile - it can be used in metadata processing to deanonymize you even if you're behind a Tor router.
No, there isn't a way to avoid going through your ISP. To avoid being detected as a Tor user, you need to use a pluggable transport. Unfortunately, there's no guarantee that your ISP won't learn you're a Tor user even when you use one, tho.
You can safely disregard the message:
All this message means is that the automatic updates feature of Tor Browser has been disabled. This is done intentionally in Tails to make sure that no security feature or configuration gets broken by automatic updates of Tor Browser.
Source: Tails documentation
In case you want to protect your communication from your ISP, the best practice would be to use Tor over VPN.
A VPN establishes an encrypted tunnel between your device and the VPN server, concealing your true IP address and your activities from your ISP and any hackers or malicious individuals who might be monitoring the network.
Using Tor with a VPN gives ...
No, the only thing your ISP can figure out and try to block is that you're using Tor network. But - never the less - it's not how it's intended to be by design: like 10-20 years before we all have had an ISP LAN direct connectivity, but now it's mostly gone for the sake of censorship. So - the only reliable way to be truly protected "in a Tor way" ...
TLDR; your ISP could find out, still they can't see what you're doing.
Your internet service provider (ISP) manages your connection to the Internet, thus receives everything you send through that connection.
Your ISP will be able to figure out that you are using Tor, as you therefor will have to connect to a Tor entry node. After the Tor connection is ...
They can see that you are connecting to that proxy. They cannot see what you are doing there, because it is HTTPS. However, it is far less secure than using TOR, because, if they seize that proxy server, they can see everything you are doing on the dark web.
There are a few ways that an ISP could learn that you're using Tor. Like you said, an ISP could easily download a list of all Tor relays and check if you're connecting to an address (ip/port) of any relay. This is the most common (and easiest) way of censoring the Tor network.
Some users run unlisted bridge relays so that censors (or in this case the ISP) ...