I am using a lot of custom connectors utilising OpenAPI files. It works terrific and opens PowerApps and Flow to many useful scenarios. I often use them between PowerApps and flow to get aroubnd limitations with the native PowerApps trigger in Flow.
I note that the OpenAPI standard supports path paramters.. eg
https://swagger.io/docs/specification/describing-parameters/#path-parameters
paths:
/users/{id}:
I also notice that the Custom Connector plumbing for Flow and PowerApps seems to have support for it... eg:

Now I use custom connectors with flow to get around limitations with the PowerApps trigger for Flow. I use a Request trigger instead and OpenAPI allows me to send rich media to Flow. Use-cases include sending photos and audio from PowerApps to flow.
Now each flow has a unique instance, so it is a good candidate for a path parameter. Ie when I made a new data connection, I'd like to be able to pass in the flow instance to make the data connection re-usable... eg:
instead of:
"paths": {
"/64f1d6xxxxxxxxxxxxxxxxxxxxxxxx8121/triggers/manual/paths/invoke": {
I have:
"paths": {
"{flow instance}/triggers/manual/paths/invoke": {
I also am using the QnAMaker API using custom connection and like Flow it has instance ID's... When I try and use the OpenAPI file I get this error:
The request failed with error: 'Parsing error(s): JSON is valid against more than one schema from 'oneOf'. No valid schemas. Path 'paths./{connectionId}/knowledgebases/{nstance-id}/generateAnswer.post.parameters[1]', line 72, position 12.'. The tracking Id is '960ec6a2-0a4f-4f9c-86a7-91518f4885a3'.
I am pretty sure my OpenAPI file is set up right. So I am hoping someone from the engineering can tell me this is supported.
regards
Paul