Hi @Hyzerberg !
Not even displayed as a Sharepoint Site, right?
As a workaround, I guess you can open any channel in your target Teams, select 'Files', next 'Open in Sharepoint'...

...so your browser will open the related Sharepoint site. Now inspect its URL. As I am doing this, since my target Teams name is MSFT, the URL looks like this:
https://myTestTenant.sharepoint.com/sites/MSFT/Shared%20Documents/Forms/AllItems.aspx?RootFolder=%2Fsites%2FMSFT%2FShared%20Documents%2FGeneral&FolderCTID=0x0veryLongId
Next, locate your TEams name and shorten the URL by removing the rest of the caracters onwards, ie.
https://myTestTenant.sharepoint.com/sites/MSFT/
Now back to Power Automete. Scroll down the options displayed in Flow 'Location input', select the very last one 'Enter custom value', paste the sohrtened site URL and press enter

Now you will be able to navigate through your site and find your target file:

Hope this helps!