Go to mixamo.com, and sign in. We're going enter the word 'Pack' as the search term This is the most effective way to download large quantities of animations from Mixamo Select the Breakdance pack. This is useful and it's got some variety. Let's download it. In the Download Settings, Set Frames per Second to 60 so we don't miss any frame data. Press download, and when that's complete, extract the resulting zip file In Blender press 'A' to select all objects and 'X' to delete them. Then confirm. Go to File, Import, Fbx Select all our fbx data, apply automatic bone orientation and import FBX The mixamo rig is selected already. Press 'M' and Select 'New Collection'. Call it 'rig_mixamo', and now this has it's own home. Ok. The collection system helps us to sort our scene contents here in the outliner Hit that little checkbox. Now we can focus on the rig. Go to Armature properties, Viewport Display, 'In Front' to see the bones within Don't worry about the strange rotations.Toggle pose mode With everything selected, hit alt-g to reset the position of the root bone. Toggle Object mode. With the mouse on the timeline, press 'X'. 'Delete Keyframes'. This mixamo rig is ready to go. Double click the object in the outliner and rename Click this plus to create a place for mixamo content. Doubleclick and rename Drag all related stuff under the 'Mixamo' collection. Don't forget to name the mixamo actions folder It's a good time to save our progress. Press Ctrl - S and save your blend file somewhere. Now activate Rigify, go to file, preferences, add-ons, and search for Rigify to activate. Add, Armature, HumanMetaRig Place in front of geo and hit tab to edit. We're going to scale this down This is the 3D cursor, and we'll use it as a pivot to scale the rig If it's not there, Press Shift S and 'Cursor to World Origin' Switch 'Transform Pivot Point' to '3D Cursor'. Select all bones and press S, drag your mouse down and click. Look at this menu Drag over the X,Y,Z values to set round up to 0.9. Snap to the front of the character by clicking over here. Notice the A and T pose is difference, we'll solve this later. let's see more with X-ray mode. Hit Alt-Z or click here. Select the face bone parent within the head bone. Press Shift-G and select 'Children'. Press 'X' and select 'Bones' to delete. Press Tab to jump back to Object mode If you want motion that is compatible with Rigify's A pose, we should press Shift-D now. This will create a duplicate as you can see here in the outliner Double-Click it and call it metarig_default If you want animation to work with the default rigify pose, we will use this later. Let's file it away. And while we're at it, create the parent rigify collection. Don't forget a meta collection Tab back to edit mode. Box select the lower arm THEN the upper arm. Snap the view to Y Change the 'Transform Pivot Point' to 'Active Element' and press 'r' to start rotating We can mirror this to the other side. Go to 'Armature', 'Symmetrize'. But we can remove this step by turning on automatic X Symmetry here. Now to hide the mesh. Expose the two meshes with the drop-down arrows. Add a collection and drag it into the rig_mixamo collection Name it 'mesh', and drag in Beta Joints and Beta Surface. disable the default collection while we're here And of course disable our mesh collection Select both hip bones then the lower spine and press G. Check the bottom of the screen These are hints on what to press in this context. Press Y, to move only on that axis Click and drag this into place and let go Activate vertex snap. Hold Ctrl and drag to Snap the top of our first bone joint to the head of the mixamo one. Continue this up the bone chain Mixamo has this one extra spine bone. We'll fix this soon Box select these bones so that we can snap them both into place. Snap the head to the base of this one, and snap the tip to the base of this end bone. select these two bone joints and press shift - S, 'Cursor to Selected.' Select this mid bone. Shift -S, Selection to Cursor. Let's come back to this extra spine bone. Press F3. This has most of Blender's commands by way of search. Type in Subdivide In the bone property tab, we'll use this text field to name the bone 'spine, dot, chest'. Select the base of the spine and hit Ctrl- L. to select most of the spine bones. Control, select the head and neck bones too Press Alt- R to zero all rotations. Continue the process of snapping our arm bones like this. Box select the hand, snap the view to Z axis and press G to position the hand into place. Set the Transform Pivot Point to 'Active Element', and shift double click the hand bone. With active element set, we can pivot from the wrist while rotating the hand into place Grab and Rotate it into place G (NOT SHIFT) - X R G And continue snapping like before. Each digit is the same process. Select from tip to base, rotate, grab and snap into place Where as, the thumb doesn't have the metacapal to worry about. But we'll get to that On our index, after setting our active bone, we also ctrl-click the end of the metacapel. With the metacapel end also selected, snap into place and start rotating. from here it's the exact same thing as the index for all other fingers. With the pinky, we're going to use S to size it up to match the mixamo pinky. As you can see here I left my snapping until the end. Doesn't really matter either way Don't forget to snap ONLY to the base, not the tails of bones.
(I'm not the creator btw, I'm just a messenger. Any questions for further help should be posted on his channel or any alternative ways he suggests.)