I fully get the issues of survey fatigue. This is about the technical limits, not the respondents’ limits.
Did you manage to get an answer to this question? I’m looking into it now as well.
You might want to consider submitting this question to SurveyGizmo Support (https://community.surveygizmo.com/email-a-support-hero/). Members of the Community forum may be able to tell you about their personal experience, but only SurveyGizmo could give you an exact number.
In my group’s experience, we once developed a survey that was 30+ pages long and had over 100 questions. It ran without a problem. The only time we ran into technical limits was with a 20+page, 50 question survey that had several skip patterns and conditional questions. Respondents with older or slower computers reported a very long time lag between pages.