I assumed that Knative [1] is the canonical self-hosted PaaS for Kubernetes. It is branded as Cloud Run [2] by Google. I'm not sure how it compares feature-by-feature with Dokku nor a 12-Factor App PaaS like Heroku.
Knative is the "serverless" (bit a weird term in this context) eventing/serving framework, and Cloud Run is a managed Knative service.
You can self-host/install Knative to your k8s cluster and the experience you end up with is pretty PaaS-ey.
Less known is this space is Rio by Rancher Labs, which is also great + similar:
Apex Up [1] deploys web apps on top of AWS Lambda using Amazon's API Gateway as the RESTful routing proxy. Maybe something like Apex Up is required to transform Knative into a PaaS for historical 12-Factor App frameworks. ZEIT Now 2.0 did the same thing for Serverless (Cloudflare Workers only?) but the company has been renamed Vercel and has pivoted around Next.js.