Vendor lock-in depends heavily on exactly what vendor you’re using and especially if it’s OSS API hosted on the vendor or a vendor API.

If you use something like AppEngine to run a Flask or Django app, you will not be locked in much because those are open source libraries with well known runtime options elsewhere.

Same to some extent with any sort of managed OSS database.

If you use something like Cloud Datastore or Firestore or DynamoDB , you are using a proprietary API and will have to rewrite all your client calls , or write an extensive shim, and probably significantly re architect to port.

Even in the “hosted OSS” option there are usually some vendor specific stuff but it can vary a lot. Something like AppEngine specifically used to be an absurd amount of API lock-in but has evolved over the years to be more of a general container runtime.