When I see an applicant for a postdoctoral or tenure-track position who has switched/is switching fields, I ask: 'why'? You'll face this question, and will need to be clear to your interlocutor about your reasons. I read CVs for evidence of mathematical strength. In young researchers, I also look for evidence of intellectual independence from the PhD/postdoc supervisors and their research program. A well-conceived move of fields is a positive here.

Consider the following:

(1) Candidate A is interested in spectral theory and microlocal analysis, and moves into numerical analysis and fast integral equation techniques because a specific problem demanded a computational approach. Candidate A then begins to contribute to NA, and takes care to publish substantial papers in reputed journals. During an interview Candidate A can precisely describe the motivating problem, and why they needed to move into numerical analysis.

(2) Candidate B starts off in microlocal analysis, and switches to math biology with no apparent link. The publications in math bio don't signal deep engagement with the new field, and aren't in the better journals. During an interview Candidate B is not quite clear about why they moved, but funding and jobs come up often.

Speaking only for myself, Candidate A's move is viewed as intellectually courageous and nimble, whilst Candidate B appears cynical. No one in field Y wants to hear that a candidate moved from field X to Y because of the money. Instead, they want to hear why the candidate finds Y an appealing, natural field to work in.