Since you have named the bones correctly with a .L-suffix you can create the bones on the right side with the Symmetrize command. Select the Armature object, switch to Edit mode, select the bones and choose Armature > Symmetrize to create the missing bones.
Then you just need to parent the Armature with the Cube mesh (your model). Make sure the Armature object is the active object (selected last). Press Ctrl+P, and choose With Automatic Weights.
Finally, switch to Pose mode and rotate the bones. Or grab the heels to lift the legs and test the IK constraints.
The cloak needs extra bones or manual weight painting else it moves with the legs.
After a closer look at your updated file, it looks like there are a few more issues. The weights are fine. Your mesh looks black in Weight Paint mode and "invisible" grey when you edit other objects because it has 6(!) Mirror modifiers on it. Besides this, there are a few other things you should fix:
- remove the Mirror modifier, just keep one.
- apply the Scale to the armature and the mesh (Ctrl+A) in Object mode
- remove 37 duplicated vertices of the mesh (M > Merge By Distance in Edit mode)
- the armature has mirrored bones for the spline and head because you gave these bones accidentally a .L (or .R) suffix. Give the suffix only bones that you want to mirror such as the shoulder, pelvis, arms & legs bones.
- the root and the control bones (IK leg controller and poles) have the deform option enabled. Enable this option only for bones that actually deform the mesh (see bottom right on the screenshot below).
- the bone rolls might be not consistent. If you rotate the arm and hand bones in T-pose the arm bends horizontally but the hand turns vertically (Yoga pose).
- for the cloak, you need to add three extra bones as you see in the video.
- todo: IK controller for the hands
If you fixed these issues then the parent operation With Automatic Weights works fine and you don't need to paint the weights manually.
Blend file with the fixes