Please help us help you and fill where relevant:
Your LimeSurvey version: [see right hand bottom of your LimeSurvey admin screen]5.3.9
Own server or LimeSurvey hosting:own
Survey theme/template:fruity
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(Write here your question/remark)Hello everyone,

is there a way do disable and/or edit the index page that lists all public surveys? I assume it needs to be manually edited since I can't find a way to do so through the admin interface.

Extend and edit the survey theme - www.limesurvey.org/manual/New_Template_System_in_LS3.x/en

This is shown in the default theme. The one that you have chosen on:
Global settings > General > Default theme

If you don't want the surveys shown on the index page, just don't choose to show them. Limesurvey only shows those surveys that you choose to.