The Streaming APIs do not currently support SRT, but this feature is in plan and is being developed.
Some of our customers are using a Nimble server or Vmix to transcode SRT to RTMP and ingest this into the Streaming APIs (Millicast) (which transcodes RTMP to WebRTC). However we do not have experience with these tools ourselves. This is also not our preferred method as any transcoding steps add on latency.
The Streaming APIs support RTMP/RTMPS and WebRTC today, with plans to support RTSP soon.