There is a new method that is working 100%.
So, there is a new version of Telegram desktop still in development. It is a version in the experimental phase, and that is why this version has a security error that causes all chat files to be downloaded without being encrypted in the folder. In other words, you can access all files directly in the folders, including files from groups/channels with restrictions on saving content.
For Mac:
For Windows:
For Linux:
All the downloaded files I found inside the directory "Telegram/TelegramForcePortable/tdata/user_data/files/" (Linux). I don't know how it will look on Windows and Mac, as I don't use them. But look for the folders and you will certainly find it.
Note 1: As I already said, this is a version that is in the development phase and is in an experimental state, so you will probably face some bugs. One of them is that in groups/channels with saving restrictions, videos do not show the download button with the file size. Then you will have to play the video and wait for it to download. After it is downloaded, you will see an option called 'Show in folder' when you right-click on the file.
Note 2: Just to be clear, this version is developed and maintained by the Telegram team itself, you may notice that the download link is hosted on the official Telegram website.
Note 3: I recommend that you use this version only when you need to download some restricted content. Don't use it as a main client for daily use.