Sounds like you had some beautiful experiences, I like to hear that! And I like how you speak about your grappling with this, and I don't think you're saying "all meaning is therefore utter garbage" - it's also satisfying and interesting to me to discuss the possibilities and share my own views from experience.
Saying a deep inner meaning is utter garbage is just a value judgement you are applying to it (maybe one point of that experience was to call you to question your value judgements and confidence in them) - the judgement is also an inner meaning experience itself that may be unqualified to judge the other experience you had - it could also be comforting to 'orphan' the experience so you don't feel the need to integrate it into your everyday reality and the adjustment that might entail. For me, I think the meaning, the feeling and the aha is real and true - but you may be misinterpreting or failing to translate the inner realization into normal consciousness. Also, whatever labels that could be applied, the utility of those learnings or experiences can also depend on context and your goals.
My issue with the part of your words saying "it was just in an altered state, it's meaningless" is why should we impose some other meaning value system from outside us, as "normal waking state" consciousness is a highly conditioned value system, taking as input culture, etc.
I believe people's first relation to the world should be their own intuition and feeling, and development of that should be the primary focus. All other value systems should be judged in relation to the primacy of that. People are terrified that means unexamined raw subconscious should be lifted to reality, in the same way they are terrified of their shadow. True experience with that process of trusting yourself indicates it's not that - it's like any other skill you must develop mastery of with time, it's nuanced - it's not binary.
Another key thing is that the information, ideas, feelings are real - but how useful they might be depends heavily on context - and most importantly - none of those things are you.
In other words, you have all these experiences, you make the meaning you choose, but you don't have to identify with any of it. You are not those things. This separation realization is a more useful way to approach these experiences than the easier and incorrect path of declaring some "utter garbage". How can you judge that? If your inner experience is utter garbage, how can you even trust your judgement of it?
Socially - an issue with encouraging people to distrust themselves or their inner states is it makes them more vulnerable to external manipulation by those who would anoint themselves authorities. "Trust me, not yourself" is classic gaslighting tactic of abusers. "Trust what I label you, not what you feel" is similarly awful and abusive. In my experience, the people who push those lines have been bad people. So take the utmost care with declaring your belief in the unreality of inner experiences!
Also be mindful of the contradiction it entails - if you declare someone else's inner experience false, wrong or untrue, you also admit that your own are similarly flawed, which undermines your very ability to determine the truth or falsehood of anyone else's inner experience, contradicting your point. It's a self-and-other-disempowering notion that can be compelling for how it encourages the surrendering of personal responsibility, yet it has to be avoided.
At the same time, taking the extreme "I must trust my inner and develop that" could be approached differently by different people. And someone's way for that, might not work for someone else. Also every is at some stage of development, if this is not a stage someone is that, they will not see the utility of it. They will be blind to its usefulness in anyway. That is what it is. You're not there, tho, you're further along.