My growth is pretty stagnant in my job and I intend to leave soon. Is it true that companies are more unwilling to "wait" as my notice period is 3 months. Should I quit or secure a job first?

Depend on your industry. If your industry is doing well and there are companies hiring, you can serve notice, send resumes and go for interviews at the same time.

By placing fixed available date rather than 3 months' notice on your resume, the potential employers will know when you can join by the latest.​​​

I'm working in my 6th job and for some instances, it really took me six months to secure the next job. So I think you got to prepare yourself mentally that if you quit, you may be unemployed for this amount of time. Additionally, with the current depressing economic climate, it may probably take you longer.

I don't work in HR, so I can't comment for sure, but your notice period of 3 months may actually turn out to be a blessing in disguise because while companies are not actively hiring at the moment, they will have hiring needs in the next quarter. So I think you should just send out resumes first.

There's also a point of view that the longer we stay unemployed, the less attractive we appear to prospective employers. So I will suggest that you tahan in your current job for now.

I wrote here about 5 things I do whenever I intend to job-hop. Maybe it will help you:
https://seedly.sg/questions/what-are-some-thing...

good luck!