What I look for is ability, passion, communication, and the ability to lead or at least be self-sufficient (or for a junior person, someone learning how to do that).
It's hard to say why you've been rejected. It sounds like you have a reasonable resume, since you've gotten a lot of interviews, even though none of them landed you an offer. So I don't think it's your resume or CV that is the problem.
There are lots of automated rejection pipelines. I have a great CV and think I'm a pretty awesome developer, and I've been automatically rejected by pipelines many times before (elastic.co I'm looking at you). Sometimes within hours on off days or in the middle of the night.
No response to jobs or automated rejection is simply part of the landscape these days. Although it's hard, don't take it personally. Put out a lot of feelers, which it sounds like you're doing.
Getting an interview is a crapshoot I think. Once you've gotten the interview, it's mostly about skill. There is some luck involved because you never know when there is a better qualified candidate also interviewing - although sometimes as a person doing hiring, I've seen two good candidates for one job, and I hire them both (sometimes for the same team, sometimes for a different team, etc.)
Why do you think you failed at the interviews? Note, giving a good interview doesn't mean that you're good at your job, and visa-versa. IMHO that's why the software engineering hiring pipeline is so broken.
I think communication and likability are key to giving a good interview, and these are skills some devs are not good at. But they are key to any job, since likely you will be working with a team, or at least a manager, who you have to be able to communicate with. If you're nailing all the whiteboarding coding questions, you might just be coming off in a bad light personally.
Algorithm challenges frankly I find to be nonsense and almost a negative signal. Instead of doing something of value, you're basically taking online quizzes. Nobody programs like leetcode or hackerrank. While algorithms can be important, I don't think it's important to be able to know the answers to trick questions. It's more important to be able to learn and pick up what you need at the time.
What you didn't mention is any internships. Did you intern somewhere when you were at school? This is how many people out of school get their first offers, and I find it's good for both sides. You know the culture, the job, and it's more like coming home than starting something from scratch. No internship is honestly a red flag for someone graduating - everyone does internships these days.
But that's water under the bridge. Call up people you knew at university and ask them how their job is going. See if you can get a referral (this is how it's really done, personal referrals get past all the nonsense, and if you have someone internal saying you're good, you basically have it in the bag).
Now if you don't have any uni friends pulling for you, I really have to think that you might just not be all that friendly, in that you might be standoffish or have some kind of personal trait that is putting people off. Ego in programmers is the worst, and if someone is mansplaining to me in the interview, I almost never hire them (pet peeve). Figure out what it is. Get another round of interviews going and try different approaches.
And if all else fails, just start your own company or something. It sounds like you've already launched things, which is definitely good. It's certainly not easy though.
Good luck.