Also, it's my little personal crusade to normalize talking about not enjoying being a parent. It's totally ok and totally normal to have these feelings. It's ok to not enjoy this. It's not ok to absolve yourself from the responsibility you sighed up for, but it's ok not to enjoy it. Especially when they're young.
My own experience is that having two kids is harder when they're young and easier when they're older.
I have friends with just one kid and it's definitely easier to have enough capacity for the kid when the kid is a baby or toddler and needs a ton of attention. Having two toddlers is exhausting.
But when the kids get older and more responsible, they can take much of their attention, socialization, and play needs from their sibling. When I've gone on vacation with friends that have just one kid, they are essentially their kids' playmate the entire trip because otherwise the poor kid is totally alone.
When I travel with my two kids, I do stuff with them, of course, but they also spend a lot of time doing stuff just the two of them.
Especially in today's Western culture where kids don't have as much autonomy out of the home to play with other kids, I think siblings are a huge help for kids getting as much peer interaction as they need. Though, of course, I support anyone who chooses to only have one kid for whatever reason.
When two are gone for some reason (sleepover, staying with family, whatever) we're always like "holy shit, one kid is barely harder than no kids!"
Feeling exhausted and frustrated with 3 or 4 young kids does not make you a bad parent or mean you're not cut out for parenting. It's a normal human reaction. People just don't talk about it much.