In teams I wanted the Wiki to be policies for people to read but NOT be able to edit

I was successful by doing the following:

  • Open teams and on the left click Teams then select your team group and go to general

  • In the upper right click the three dots and click Open in SharePoint

  • Click the Setting gear in the corner and go to Site Contents

  • Click Teams Wiki Data

  • Click into the Channel Folder you want to restrict edit access to (e.g. general folder)

  • In the lower left corner click Return to Classic Experience (I had to click this twice)

  • You may have to trial and error here but on the left click the long guid number with _wiki at the end (I did the first one and it worked but you may have to try others)

  • On the right click the info icon

  • Click Manage access and click the down arrow near the members section and click Can View

  • Once you find the right userid_wiki go back to the channel as a member and try to edit the Wiki
  • You should get an error like this if it is Read Only

Reference: https://techcommunity.microsoft.com/t5/microsoft-teams/teams-wiki-where-is-it-stored/m-p/143827