Instead of overwriting the irc.server_default.capabilities config option, use the new irc_cap_sync_req modifier to request the extra read-marker capability.
Checklist (script update)
[x] Author has been contacted
[x] Single commit, single file added
[x] Commit message format: script_name.py X.Y: …
[x] Script version and Changelog have been updated
[x] For Python script: works with Python 3 (Python 2 support is optional)
Instead of overwriting the irc.server_default.capabilities config option, use the new irc_cap_sync_req modifier to request the extra read-marker capability.
Checklist (script update)
script_name.py X.Y: …