If it's a quality DM and a quality campaign it will be harder to get into because a good DM knows that it takes a little effort to figure out if a player is a good fit.
I usually get about 5 to 10 applications every time I post an opening in a game, but I also have a very long list of rules, and I require a specific application process which weeds out most of the lazy people. I have a job and a life, and it takes time to vet people, so sometimes I may get 10 applicants and not pick any of them if what they posted in the app doesn't really impress me or doesn't seem like a good fit. Usually people who talk a lot about their character rather than their self as a player annoy me. If I can tell that somebody is intelligent and genuine and creative or interesting or fun, I will privately message them through roll 20 and give them my contact info through discord. So watch your private messages. When they respond I set up a discord interview to just talk to the person to see if their personality is a good fit and to make sure they're not psycho (there's a lot of psychos on free internet sites). Depending on where the campaign is, I'll spend about 15 minutes to 30 minutes talking to the person mostly just about their interests in the hobby, and only a little bit about the campaign. If I like the person the next step is to find out more about their character and how that character will fit into the world. It's a little bit different when it's a brand new campaign, but at this point I've made so many friends over roll 20 that I never have to crew up from scratch, so it's usually just adding one to two people to the mix.
When people privately message me I just ignore them because I clearly state in the posting on the LFG page how to apply. Annoying people do not make good players, so don't be annoying is my best advice. And be patient, and try to apply to a few different games rather than putting all your eggs in one basket.
If the DM hosting the game doesn't have a label such as pro or Plus it means they are not paying for the account which means it could even be a not so serious posting like they were just experimenting with the game. Usually if the DM writes a lot about their game it shows they care and you are probably going to have better chances to get into it.
My best best advice is to do the same thing I did: run a game! Start with a simple one shot. You can buy one or make one. I made one and actually ran it 17 different times because I wanted to fine-tune it and practice my DM skills in a sort of controlled environment. I also designed it in such a way that it teaches people how to play the game and how to use roll 20 in a single session. That's what worked for me, then I made new friends and got invited to a campaign.
Keep applying, but try to focus on showcasing your personality and creativity in a not so annoying way, don't spend a bunch of time talking about the cool character you made up unless the DM specifically asked for that. It's okay to say that you might want to play a gnome artificer or whatever. Try to focus your energy on demonstrating the value and fun that you would add to the group.