It’s not an either/or thing.
It’s like asking “Can I get a date with a pretty girl when I’m poor, slovenly, and out of shape, or do I have to be rich and look like Brad Pitt?” Sure, anyone can, but the more you lean towards that latter, the easier it’s going to be.
In theory there are jobs out there for people that have just begun FCC. There may be some company that has very low standards and are willing to work with someone, and pay so little that it makes sense to them, or maybe that person just interviews really well - it does happen. The question is - Is it likely? The more you learn and do, the odds of getting a job slowly increase. And at a certain point, it’s time and persistence.
it can’t be true that everyone is a math whiz
No, many aren’t. And people overestimate the importance of math, like you have to be a math wiz. For the vast majority of web dev, if you’re comfortable with the math they teach 12-year-olds, you’re probably fine.
Should I just apply for jobs even when I feel like I am not ready yet?
Prereqs in job postings are often wish lists, often unrealistic. If you halfway meet their requirements, it would probably be good to apply.
If you are working through the FCC material, I’d say that after the first 3 certs, you are probably beginning to become reasonably employable. After the first 6, you have a good tech stack. Granted, it will still be very, very, very difficult to get that first job.
When do you know you are ready to make it professionally?
You’ll never feel ready. It’s a process of never ending learning and always feeling at least a little inadequate.
Just keep learning and building stuff.