Pokestop didn't appear even after 2 days of approval but Ingress portals are live

Solution 1:

Niantic is currently upgrading all of their backend systems to the latest version of Lightship, which is preventing the waypoint sync systems from running effectively. Here's a direct quote from their most recent update.

Due to upgrades we are making to the backend, Portal nominations, and photo submissions and edits will be delayed for several weeks, and we are actively working to address this. Please note that you do not need to submit these nominations/edits/photos again.

Under typical operation this data would sync 5 times per week. My guess would be that this upgrade was started in the short period after the Ingress portals went live, but before the regularly scheduled synchronisation process ran, leading to the waypoints appearing in Ingress but not in Pokemon Go.