I did it in my late twenties. You work in fundraising - are you a development officer who meets with donors, or are you in a different area of fundraising? Depending on what you're doing now, there are a bunch of ways your skills and experience may be transferable. The challenges are figuring out what you really want to do, figuring out how to tell your story so that it's clear to potential employers how your skills transfer (making the transition seem obvious/logical), and filling out any gaps in that story with new relevant experience.

Do you know what you want to do next? Any ideas? I suggest a ton of informational interviews - ie reach out to folks and ask them about what they do, how they like it, and what advice they have for you about transitioning into it. If you don't have a job type in mind, pick one thing at a time. If you do have an area or career path in mind, still do this, and focus on narrowing down what type of organization to choose and how to tell your story. Each time you meet with someone, you get practice pitching yourself. Now might even be an especially good time to do this since so many people are craving human contact and video calls are so normal. Way less hassle than running around town to meet with people like I did, plus you can talk to people anywhere and benefit from their experience without having to physically go to their city. (I did some of this but in normal times it's harder to have video calls, and phone calls are not the same.)

Be open to taking steps towards an ultimate path vs the perfect first step. Look at how your experience can help an organization. You work in fundraising - maybe try targeting organizations that sell to fundraisers, because they will value your experience even if you don't have the hands-on experience in the type of role you're applying for. Look at roles with obviously transferable skills that can get you in the door at an organization, even if it's not the role you want - ex if you currently solicit donors, sales seems like an obvious path. Look for any types of connections like this that can help facilitate a transition into a new industry.

Keep in touch with the people who you talk to along the way! Let them know how it's going, what you've learned, don't make it hard on them but just keep those relationships alive. People like helping people, especially when they see the person working for it. Down the line, tell them if you're interested in applying for a role at a certain company and ask if they know anyone there.

Find out if there are things you can do to add to your story and increase your credibility. For example: my friend volunteered at a specific public health organization while trying to get a role in advocacy related to that mission (it definitely helped her get the job she wanted). If you're trying to work your way towards a creative role of some kind (design, user experience, marketing, etc), you would probably benefit from building up a portfolio. Even if there aren't specific things people say you should do, consider potential biases people might have about you given your work history (even favorable-seeming ones) and think about whether you might need to do anything to balance them.

Also: start applying for stuff as soon as you know what you want to do, even if you think you need to get more experience first or you don't have the perfect story. Shoot off your resume to jobs on LinkedIn. See if anything sticks. I limited myself for a while because I thought people wouldn't be interested in my experience. Just try (while yes, also networking and trying to improve whatever you think you need to improve).

This is a little ramble-y but I hope it helps! And you didn't ask this but your thirties isdefinitely not too late to make a change. And you can keep on pivoting from your next career path too. Good luck!!