there seems to be bug in Grid-format default settings.
When changing Course display default (format_grid | defaultcoursedisplay) in global settings to -> 'Show one section per page', that setting does not become the default setting when creating new course with grid-format , nor there is option to reset older grid-courses to that setting.
Moodle 3.5.12 (Build: 20200511)
Grid plugin->version = 2018052306
Moodle 3.8.3+ (Build: 20200609)
Grid plugin->version = 2019111700;