Here's a quick guide, it may cover stuff you already know.
This mod does not include any portraits, you need to download them separately and put them in the AppData's "portraits" or "bodies" folders.
This mod should be extracted from the zip archive into the AppData's "mods" folder. Be sure that the path fits the form of "Strive/mods/<modname>/info.txt", as it will not install correctly if there are more or less folders in the path. (If the mod is in the folder named "randomportraits1.0", then it is probably wrong.)
Once in place, mods are applied to the game through the "Mods" panel located in the game's main screen. Select the mods to be applied, then press "Apply". The game will attempt to apply the mods, but will not inform you of any problems that occurred. Thus, mods need to be verified manually. This mod can generally be verified by loading a progress, select a slave, open the Customization tab, and look for the "Random Portrait" button. If present, then the mod has successfully been applied, though it may still conflict with other mods.
Viewing post in Improved Random Portraits v1.0
"info.txt" is a file located inside mods that provides an explanation of the mod. If you have "randomportraits1.0", then you have too many folders. Look inside that folder, you will find the folder "randomportraits", and inside that folder you will find "info.txt". You need to remove the contents of "randomportraits1.0" and put them into the AppData's "mods" folder. That way AppData will have a path containing "Strive/mods/randomportraits/info.txt".
Okay, this is good information; however, based on that the mod was most likely not installed correctly, as the presence of the random portrait button is the simplest sign that the mod has been installed. The fact that you can select portraits manually means that there is probably no issues on that side.
You have probably seen the install instructions I gave a few posts above this, please be sure that you have followed them carefully. I'll try to give a detailed list of things to verify.
On windows, there should be a file path "C:\Users\USERNAME\AppData\Roaming\Strive\mods\randomportraits\info.txt". If correct, the contents of that file will display on the right side of the panel when you hover the mouse over the mod name in the mod panel.
Press the "Active Mods" button on the mod panel. Near the top left corner of the mod panel, the text "Active Mod List" should appear as part of a transparent popup, with "randomportraits" underneath. (The visibility of this popup can be fixed by my bugfix patch on the Strive Discord, but it will not effect whether the mod works) If the mod is not listed, then try applying the mod.
In the folder containing game files, find and open the game file "Strive\files\scripts\mainmenu.gd" with any decent text editor. Find the line "globals.constructor.randomportrait(startSlave)", it should be just below the line "func _on_slaveconfirm_pressed():". If that line is not present, then the mod system did not add the mod to the game files. You may need to move the Strive game files to a new location or change the permissions of the folder to allow the game to change it's own files. A user once had an issue with permissions due to the game being located in the standard "Program Files" folder.