This might be useful for some. It has just been posted in another group the requirements for a Residence Certificate in Chiang Mai. Note - different Immigration Offices have different requirements so check what is required where you apply.
TLDR : Answer Summary
The post highlights the varying requirements for a Residence Certificate in Chiang Mai, noting that different Immigration Offices may have different requirements. A comment mentioned that in Phuket, one of the requirements (number 3) might not be necessary, and another questioned whether only the first page of the rental contract is needed.