1. Go to any YouTube channel you wish to subscribe to (such as youtube.com/user/YouTube).
2. View source.
3. Search for rssUrl or channel_id.
https://www.youtube.com/feeds/videos.xml?channel_id=UC3x6qC4...
As for the comments that's likely a bigger issue to tackle, especially with how liberal Google is with captchas these days.
do you do this personally? i've tried and found the barrier for entry is through the roof. if you don't configure everything just right you end up on gmail's spam blacklists and nobody gets your emails. and good luck getting off the blacklist once you're there.
i would love advice from anybody for self-hosting a reliable email server that the major carriers won't treat as a second-class citizen.
The barrier to entry is certainly higher than setting up a web server, but it's not too hard.
Advice for improving deliverability would be to add SPF and DMARC records for your domain (don't worry about DKIM).
Other than that, if I end up in someone's spam filter, I tell them to fix their spam filter. If your spam filter is classifying legitimate emails as spam, it's a bad spam filter. Doesn't happen often though.
They can still collect all the info you provide them directly, but it's a bit different than cross-referencing your gmail account with your phone's location history and your google search history, paired with your Google calendar travel plans and emails about shopping list updates for your Amazon account.
I'm using that email for ~6 months now, I haven't yet send an email to gmail... I checked. And I use email quite a lot actually.
The store itself isn't the only functionality; many apps rely on many services provided by Google's proprietary Google Apps (Gapps) and most users will need to work around that too; there are FOSS replacements such as the microG project (I don't know its current state).
Completely free, uses none of the google internal APIs and manages your subscriptions, watch and search history locally.
Replace file storage with a hard disk you control.
Replace chrome with chromium (or, better, firefox).
Replace android with an android fork that uses f-droid instead of the Play store.
And you're done, no more Google usage.
I currently use my Google account only for signing in to YouTube, so that it keeps track of my subscriptions and let me write comments. I use Firefox's "multi-account containers" so that only the "YouTube" container knows my Google account. Google Analytics for non-YouTube sites doesn't get to trivially associate me with my Google account, because I look at all other sites in different containers.
If someone created an alternative YouTube interface that allowed you to keep track of subscriptions without telling Google who you are, I'd probably use that rather than logging in to YouTube. Bonus points if it also gives you a disposable Google account with which to write comments.