When I post a conversation in Microsoft Teams and attach files to the conversation, the files are saved in "Files". But can I decide to save the files in a specific folder (of course in the same Team)?
If you upload from your computer into a channel conversation you can't select a folder to save the file to in Teams. But you can upload the file first and then select that file in your conversation and select Share a link.
Or you can upload a file in to a folder in Files open it and start a conversation from that file, that conversation will be posted in the channel.