For me finding the right therapist took some amount of trial and error. There are a lot of factors in what makes a therapist good, and what makes a therapist a good fit for someone. I think that personality is probably the most important aspect and that is something you won't know until you've had a few sessions with someone. I've seen some therapists who were really pleasant to talk to. It was like venting to a friend (for $140 an hour). But it wasn't really "working" because there wasn't any growth. I eventually learned that beyond looking for someone who is compatible personality-wise, there are a lot of questions that can be asked up front that will give you an idea of how effective a therapist will be.
What is their background and experience? Where were they educated? Why did they want to become a therapist? How long have they been practicing? If they're comfortable answering basic personal questions (and it matters to you as the client), are they married? Do they have kids?
How many clients do they see regularly? Do they truly have time to take you on? What is their preferred method of communication? Is after hours communication an option in the event of a crisis? Do they handle booking and billing or do they have an assistant? Are virtual sessions an option? How do they ensure privacy within sessions (ie white noise machine outside the door, extra soundproofing)? What about confidentiality?
Do they have any areas that they specialize in or work within the most? Couples counseling? Blended families? Addiction? LGBTQ issues?
What type of therapy do they offer? CBT, psychoanalytic, humanistic, etc? What about treatments like EMDR?
Is their practice informed by any specific worldviews, such as religion or culture? If so, (and if applicable) are they able to effectively work with a client who has different beliefs or customs?
I've been seeing my current therapist for two years now and he is a great fit. I initially chose him because I hoped that my husband would join me in therapy and I knew he would only respect a male therapist. I never would have gone to see a male therapist just for myself because I assumed it would be too awkward to discuss certain things. But it was just me, and it turned out I actually really needed an assertive male therapist who wasn't afraid to challenge me and definitely wasn't in it to just be a friendly sounding board. And the awkward things can be slightly uncomfortable, but it's worth it because I've grown so, so much. This is one of the reasons why I always encourage people to be willing to try a therapist who is just a little outside of their comfort zone.
Anyway, hopefully something in this novel is helpful.

Good luck!