Can I switch a size chart off for a while without deleting it?

Yes. In Plugins → Size Charts, click Edit on the chart, untick Active and click Save. The list then shows it as Off, and it stops appearing on product pages. Your table and assignments are kept, so tick Active again when it's ready.

To hide every size chart at once, go to the Settings tab, untick Show size charts on the storefront and click Save settings.

If a product is also in a category with another active chart, that chart shows instead while this one is off.