In your TS3 user game folder in Documents, which is presumably where you have added the Mods folder framework, there will be a file called DeviceConfig.log. Depending on your operating system file name display preferences, it may show up as just DeviceConfig but it's the same file. Don't open it, but right-click and do Properties (or Get Info on a Mac). The modification date/time should exactly match the last time you started up the game. If you aren't sure when that was, start up the game and the date/time on that file should update instantly. If the date/time is stale, that means you have another TS3 user game folder on your system someplace, the user game folder to which you are adding mods is not the "live" one, and the game is ignoring it. On Win 10, OneDrive is a common place for extra unwanted game folders to be hiding.
If that's not it, meaning the date/time on that file is updating properly, then we will need to see three screenshots, one each, that show your TS3 user game folder, your Mods folder, and your Mods\Packages folder and their contents in Detail View so we can help determine if the setup is correct.