Issues with finding ingest-server URL for particular stream that is live or going to be live

No.

Streams are not “scheduled” and recieve a specific URL like you do on YouTube.

Pick an ingest and just go live.

additionally no, you cannot determine the ingest a given stream is using.

If you are the streamer you can know via inspector - (https://inspector.twitch.tv/) or the fact you know from putting a given URL into your streaming software.

There is no way to get what ingest someone else is using.