Unfortunately, living in a country where meeting any kind of people at all is extremely hard to start with, I barely get a chance to ever even flirt or ask a woman on a date.
At least your friend is getting rejections. That means he somehow managed to figure out how to routinely get in contact with women.
Going to the gym helps with both of these problems. The gym is a place you can meet people, being fit makes you more confident and makes it easier to meet people, and being fit gives you attractive qualities that are in plain view.
My wife has to put up with all sorts of weird behaviour (staring, unsolicited advice, chatting up, following around the gym, and occasionally somebody trying to leave with her, which cuts my workout short) just to get a workout. If we didn't live in such a small living space, we'd build a home gym to get away from public gyms.
I know you're not advising that, but I think more-or-less the gym isn't an environment for meeting people, unless it's truly a per-chance meeting where neither side is actively looking for anything.
One thing that seems to work is to find an activity that you like, which will also be done along with a significant number of single women[1]. Then just do it and have fun doing it. People are more attractive when they are having fun and less attractive when they are desperately searching for someone. It also gives you a shared interest, which is a natural starting point for conversation. In the worst case, you are having fun, in the best case you will meet someone.
I have had exactly zero relationships successfully start via the stereotypical "someone set us up" "meet at a mixer" "online dating" methods, despite several failed attempts at those. Everyone I went on a third date with was via me doing some activity where I wasn't looking for a date.
There are plenty of things that are out of your control that can sink a relationship. A surprisingly large number of women will flatly refuse to date someone who is shorter than they are, which sucks for short people.
1: A sibling comment suggests Zumba classes. Using this as an example: If you go to a Zumba class obviously looking for a date, you are likely to come off as a creep. If you want to get cardio exercise though, taking a Zumba class instead of buying a treadmill to use at home is going to give you a lot more chances to meet someone, and is a similar time & money investment, so you lose nothing if all that happens is you get fit.
I found the book 'Models' by Mark Manson to be a big help. Sometimes, the right advice really does make a difference.
If you're having trouble dating, not because you can't land a date but because all the dates disappoint you, it might be time to evaluate whether or not you're realistically setting your standards. People aren't like an RNG where you can roll and roll and roll until you get your perfectly desired stats. It's more like people will always have bad stats and you have to figure out if you can live with it.
When I realized that I don't actually care about most of those things, I just was being reminded of previous bad relationships, it became much easier to figure out the things I actually cared about.
I have a friend who has the full puzzle and can’t seem to put it together. Used to be fat, poor, lived with his parents. In five years he’s completely turned his life around - he’s young, in shape, has a career, and is moving out into his own place. Still can’t get a date. Starting to both rapidly lose his hair to male pattern baldness and his sanity to the numerous rejections he receives.
This isn’t some comment on society or my friend, I’m pointing out how nobody (especially him) seems to know what he needs to be happy. If even specific advice doesn’t work how could generic advice ever help?
Godspeed friend, hope things get better for you.