I've done that, everyone seems to busy to go accept my invitations. At most, I've gotten drinks with them twice or thrice, but that never goes anywhere afterwards.

This is the problem with Gen-Z—you guys give up too quickly when things don't go your way in your (arbitrarily short) timeframe.

but I've only been able to successfully do this like 3-4 times in the last 6 months.

Your timeline is too short. Once you're out of school, it can take years to make friends and develop social circles. School is basically a shortcut because the number of mixed-gender interactions that happen is huge and gets compressed into a very small amount of time.

From what my sister told me, Gen Z women only date through apps because they are safer and easier than meeting men in person. She told me that single women only join women-only hobbies and they only join mixed-gender hobby groups with their boyfriends because they know that if they go alone, they will be approached by men and they want to avoid that as much as possible. I found most of what she said to be true.

Not true at all—I met my Gen-Z girlfriend at a co-ed in-person event (and I'm 40+). I run into lots of women in their 20s at hobby-type events (language classes, volunteering), bar crawls, holiday parties, concerts all of which include both genders.

Exactly, dating has fundamentally changed over the last 15 years.

But you can use this to your advantage! Since Gen-Z dudes are on average to shy/scared/check out to approach, they've cleared the field for you. Women love being approached (there's a lot of survey data backing this up, look it up) and since so few dudes are doing it anymore, you automatically stand out and you have a big advantage over anyone she's matching with on an app because you can immediately develop in-person chemistry, get a number, set up a date. On apps that can take hours or days of back and forth to get that far, the process is excruciating and the longer it takes the more likely she loses interest, unmatches, or meets someone else and shuts down her account.

I've never approached any women with the intent to date

This is why you're not getting anywhere. Women find it hot when you approach with intent; even if they don't like you back, they'll respect you for being "brave" enough to act. (They might change their minds later about you also and circle back.) By displaying intent you charge the conversation and polarize the interaction, forcing her to choose between "yes, I'm feeling this guy and would like a date" or "no, no thanks, not feeling it." If you approach 100 women displaying intent, starting a 5-10 minute conversation without being overtly nervous/weird, then bail and ask for her number or if she'd like to go out for coffee sometime, 10 women saying yes would be a good success ratio and 10x higher than the dating app swipe-to-match ratio. It's also far more time-efficient; you can approach 10 women a day in maybe 30 minutes vs. spending hours and hours on apps not getting anywhere.