I think my parents can have quite rigid thinking, certainly. I sometimes get very racist, homophobic vibes from them but other times, they surprise me. I feel like my parents have a much greater sense of obligation than I do. They take pride in their house and garden. They both worked hard and had careers.
In some ways, my living situation is in rebellion to that. My environment is a mess. My 'career' is very precarious and I've reached a point that I don't even care as much. Although, enough to promise myself that I won't become a burden on them. I'm in my 40's. I don't have much excuse.
But ultimately- if we fail in life, that likely means they will have to support us. We know they didn't do that to their parents (presumably) so, I expect that's one reason they get annoyed/angry. They maybe felt like they had no choice. (Of course, they did- they didn't have to have children and create that extra burden on themselves to begin with.) But- either way, they chose to not be a financial burden on their parents (presumably) so, they probably do expect us to do the same. I don't know if that relates to you though... depends on whether it's looking to your Mum like you will reject work and education leading to work and rely on them.
My Dad also used to get kind of frustrated when I started talking about the meaning of life- usually from a pessimistic stance. He said that he went through that 'phase'. Some parents will see it as a phase or, an act of rebellion that you will grow out of. I guess as well- seeing as we don't have answers on the meaning of life, they must have maybe come to the conclusion that it wasn't worth their time and maybe was only making them miserable.
Here's how I see it. No matter how good we are at masking, our parents can likely tell that we're not entirely happy. So- in a way, they likely will criticise whatever it is we've gotten ourselves mixed up in- philosophy, social ideas, religion, gaming- could be anything. They'll sense that we're depessed and blame whatever it is we're focusing on as the cause in a way. A mother once came on here to ask whether people thought excessive gaming could be making her son depressed. The consensus was- no, your son is likely spending so much time gaming because he is depressed and he's trying to escape.
I think, when we feel down, we seek out things that resonate with that- like this forum! So- while it isn't causing the low mood, it's debatably feeding it. Which is something else your Mum may not like. So, it may not be just the ideas themselves your Mum disagrees with- although, she probably does as well! She may just not like the idea of you getting so 'bogged down' with lots of pessimistic ideas about the world.
As my Dad saw it- he didn't have the time or 'luxury' to think about all that stuff. He was too busy earning money for his family. The 'problem' I guess with people like us these days is we've chosen to reject a lot of that and, we're questioning it all. In their world though- that made sense. They had to become independent from their own parents. It was expected of them. Either they wanted a family or, that was expected of them too. In our cases, it depends on whether we are comfortable being financially dependent on our parents. A lot of people here are anti-natilist.
But of course- the option that our parents may never have seriously considered. That I expect many would be horrified to know that we are considering- is that we may kill ourselves. Everything changes with that idea. If you knew you couldn't kill yourself- maybe (for your own sanity,) your ideas would be more caught up in trying to live a reasonable life rather than the meaning of it all etc. That's their reality. They likely know they won't ever find out the meaning of life. They know they're likely here for a while. They feel responsible to care for their children and I guess, they just make the best of what they have. My Dad avoids things that make him unhappy or uneasy. It's more about escapism now. I think seriously considering suicide as an option is one of the major things that separates us from them.