This is something I'm really familiar with. If you're ever bored and wanting someone to chat with, I'm available :)

i know how it feels. even when ppl are excluding me with good intentions (like not inviting me to outdoor/sporty stuff cause of my legs) it still sucks. but whats important is to remember that you are not the problem. nor are you A problem.

I do that a lot too. I'm also really bad at starting conversations TwT

That feeling sucks so much man...

I used to get that often but... it often came to me over-thinking stuff.
Most friendships some do nowadays can be online, making friends as an adult face to face ain't so easy after all.
When it comes to feeling left out of things, it quite often can come down to timezones or the others juggling through so many peeps that they may forget, it wouldn't hurt to poke and ask sometimes.
Being unable to connect is normal and everyone experiences it nowadays to a degree I feel, it's just how things are with how society is.
And "meaningless" is quite subjective, it's about as meaningful as you want it to be I believe, sure it also matters what the other end feels but... 50% of it is on our side of the net so to speak.
As for other people doing it effortlessly; social butterflies do exist but those people usually have countless acquaintances with no real connection but still just a few friends.

I don't think you're the problem, I've barely gotten to meet you to be fair but from the little I've seen you seem like a very normal person, maybe just a bit shy (and that's a lot of speculating on my end).

All in all if I can give you a suggestion... sometimes it's best to not overthink things, take them at face value. Say when someone leaves you on read 99.9% of the time the usually just got pulled out, and the same type of logic applies to most cases. Trying to reach out to others more often, talking on the daily, etc does help too.

You are definitely not the problem, socialising is a fickle thing and needs a lot of energy, especially for more introverted people. I know that from personal experience.

It seems effortless from afar, but every good friendship is build on a lot of time and attention for each other. And not every quick seemingly well-working contact is meant to hold forever. We usually only see episodes in social interaction of other people, but everybody has difficulties and stress sometimes.
That's why I think comparing to others doesn't help to feel better, it's about you and you need to feel comfortable with the interactions you have. Sometimes it takes a while to find suitable people and stable connections, especially via the internet it's veeery difficult to keep things going. But when it clicks, it's certainly worth it.

I prefer to have a few well-working connections, quality is important to me instead of quantity, especially with a busy life. I am sure can make good connections over time too, you are certainly not the problem, socialising is just no easy task in general.