I'd like to start running the test suites with the asyncioreactor enabled to see what breaks. This issue tracks the changes in Synapse, Sytest and Complement to achieve this.

Related: #8642, #12135

I opened a few PRs:

• Parse SYNAPSE_ASYNC_IO_REACTOR env variable & log the reactor on startup #14092 which is required for:
  • Allow running Synapse with the asyncioreactor enabled sytest#1301 which is required for:
    • Add Sytest jobs with the asyncio reactor enabled #14101
  • Allow enabling the asyncio reactor in complement #14099