skyscanner shows that from Oct 31, there will be flights from Hong Kong to Chiang Mai operated by Hog Kong Express, hope it will materialize.
https://www.skyscanner.com.hk/transport/flights/hkg/cnx/211031/?adults=1&adultsv2=1&cabinclass=economy&children=0&childrenv2=&destinationentityid=27539873&inboundaltsenabled=false&infants=0&outboundaltsenabled=false&preferdirects=false&preferflexible=false&ref=home&rtn=0