In addition to the excellent advice above, I wanted to build on one aspect that I’ve found helpful for my S23 (and ultimately helpful for my own anxiety when I was in your shoes).
It aids both your child and you to transition your parenting (as much as possible) towards “helping them help themselves” and being a sounding board and observer first, and giving advice second (and giving that advice in perhaps a more Socratic way, e.g.: what do you think about ____? Have you considered…?).
There are support systems in college, and it’s essential that your child knows how to identify an issue, what to do about it, and who to talk to, and what steps to take to access support. But we have to teach them how to do that. 
So if your kiddo wails about a situation this year, refrain from saying what you think they should do, and instead ask: ah, what do you think you’re going to do/who do you think you might talk to…etc.?
If/when they’re totally at a loss, demonstrate breaking things down into smaller pieces, asking questions to help steer them towards thinking these challenges through themselves, instead of providing the answers.
And really take the time this year to ensure they know how to write emails to teachers (and future professors) and support staff in a way that’s polite and productive: e.g. clearly describe the issue or request, then state specifically what you’re requesting for (e.g. a 30 minute meeting to go over [a concept], or 10 minutes to talk about X, or an extension on an assignment, etc.), then put out options (e.g.: name 3 prospective times that you could meet) and then ask the recepient what would work best for them. (And explain to your kiddo how productive emails like this will get your kiddo faster and more helpful responses overall.)
Work with your kiddo this year on how to email their doctors with questions, how to set up appointments with their healthcare providers on their own (and how to do a quick video consult, too). If they’re not already doing their laundry, teach them how and have them do it the rest of this year.
The 12th grade year is hard for parents! You will feel (a little!) bit better if you know that you’ve prepared your kid with the soft skills for this next stage in their lives. Did my kiddo have a perfectly perfect easy peasy first year of college? He didn’t! But when he did have a hiccup in spring semester he knew what he needed to do, he knew who and how to contact the people that could help him, he knew how to make specific and polite requests of professors, and it all worked out. In his experience there are a lot of kids who don’t know how to do these things, and he was glad we’d gone over it so many times while he was in high school.
12th grade is full of emotions for parents; you will get through this and things will work out. Just keep breathing and break things down into small steps and you’re going to be okay - hang in there 