I worked at a company that sounds similarly to this company culture about 3 years ago. I got laid off, moved onto a better company.
But just yesterday I ran into someone who works at my old company. We chatted for a little bit until I realized how drained I was getting just from talking to him

And I learned something about this type of culture, especially having read these comments in this thread:

Canonical sounds like a tech fraternity. Just imagine a traditional fraternity or sorority - the hazing (the boss eating food during your interview), the induction processes (hiring asking for high school background, the unnecsesary long essay prompts, unnecessary long interview process, the ghosting, etc)

They are filtering for a very specific person. Someone who is a "Yes" person to the point that they will demolish their morale values and respect on themselves. They sound like there looking for more younger & naiive, but brilliant engineers, that can be basically exploited to build great things. Asking for so much personal information about why they want to work there, there high school background, is basically from the HR perspective "Can I exploit this person if they work there, by leveraging their past against them?" It's a power play dynamic - it's easier to manipulate and gaslight someone you know more about

I have people on both sides of these spectrums.

On the applicant side, we sometimes call them 10x genius engineers that make everyone's life miserable because their code is way too complex for no particular reason. There also underpaid usually and promised promotions and payraises, but those are just empty promises to keep them on the leash. They say their coworkers code is dogshit but don't realize how many unnecessary abstractions that made in their own code. They also don't take advice from friends telling them they are being exploited either, and they usually have an addiction problem to compensate the exploitation (weed,drugs, alchohol generally speaking). They also do amazing work and build amazing things though on the other end, and usually invent very novel solutions that aren't easy for others to inherit or work on

On the business/HR/CEO side - these are the same people that never mature out of the applicant side, and continue the hazing process ritual. Usually the boss on the outside sounds very down to earth, respectable, but deep down inside he likes to have raging parties and feels like he/she missed out on the frat lifestyle growing up. It's externalized validation for them

Having a particularly confusing hiring process is actually a form of gatekeeping from keeping people that respect their boundaries from applying. It's the same level of logic as scammers who will intentionally misspell their emails to filter for people who aren't as grammatical or tech savvy - for instance, since it's easier to target more gullible or less-informed audiences

Not saying that Canonical is that case. But it definitely does sound like a tech fraternity. And the hiring process sounds like a hazing process at a fraternity.
But, at the time I actually really wanted that tech fraternity life style and appreciated it for what it was. Most small / tech consulting agencies are more likely to have this cultural mindset, because working with new clientelle usually is an emotional rollercoaster. You do learn a lot in these environments - and it is stressful - and you do get treated like dogshit without you realizing it (someone outside the company has to tell you) - but you also learn to appreciate a more mature better work/life balance afterwards.

It's not terrible for a first job if your young single and have no kids, sometimes you have to learn things the hard way