Flow has no native triggers for blogs or comments activity.
Nor does it seem there's any purpose built connectors for blogs or comments, afaik:
https://help.shopify.com/en/manual/shopify-flow/reference/connectors
You would need either to build a custom middleware app to have a custom flow trigger.
https://shopify.dev/apps/flow/triggers .
Or use an app like arigtao, mesa , or usemechanic to script either the flow trigger or do the full automation over the api possibly in tandem with frontend javascript customizations.
https://tasks.mechanic.dev/demonstration-shopify-flow-integration
https://learn.mechanic.dev/platform/integrations/shopify-flow
If needing that solution explored contact me, info in sig.
Please provide context store url, post url and project detail.
