Guest users not having the ability to search files in Teams is problematic. It's the number one requested item in our group with over 100 guest users. They navigate to SharePoint and search files without issue. Currently using the search feature in Teams only returns the "People" and "Messages" tabs, the "Files" tab only shows for non-guest accounts.
Really need to look into this because I see several threads on here about adding guest users, without a search feature for guests its a struggle with the users as they want to user other products because of this missing function.