There are a few ways to get a mentor if you search in the right places.
1. Mentorship programs
There's a mentorship program every few months where mentors can choose people to be their mentees. It has mentors for Standard, Mania, Taiko and catch. The latest cycle started back in June a new cycle may start in September or October. Keep in mind that this is the most well known way of getting mentors so there's always a lot of mappers trying to get one. Here's the link to the forum post of the last cycle if you want to look into it
home/news/2025-06-09-community-mentorship-program-summer-2025-signups-now-open.
2. Asking more experienced mappers.
Most mappers would be happy to help someone new out. That's just how the community is. Try asking around in osu mapping discord servers or you can even try to dm mappers whose maps you like. This is harder than the first one since not every mapper has the time / want to have mentees.
I only know of these 2 ways to get mentees. Personally, I'd say that having a mentor can be really helpful, but not necessary. You can still improve without one. Most people I know never had a mentor but they are still doing well.
My recommendation would be to ask mappers whose maps you like for feedback. Mappers would always be happy to hear that people liked their maps or got inspiration from them and people are more than happy to give some quick feedback on maps.
Joining a discord server can also help a lot. Asking other mappers for feedback is what helps you get better at mapping after all.
That's about it. If your goal is to get better at mapping then a mentor isn't necessary, but some extra help. Just keep on mapping and asking for feedback and you'll see yourself improve over time. Have fun mapping and I hope I could be useful.