Literally the "data" option on the launcher for Morrowind, the OG Oblivion, Fallout 3, Fallout: NV, and Skyrim... The order can also be manually adjusted by just moving the loaded files higher or lower on the screen (or manually editing the ini file that controls load order).

Only FO4 and Starfield are missing this, opting instead to have the Creation Store UI replacing it with such poor implementation I haven't been able to manually install mods on either. They're the only two I absolutely need a mod manager to manage my mods with.