Diaclone Reboot Big Powered GV has notoriously difficult to remove lower legs. This replacement clip can reduce the force required to unclip the legs, or replace a broken clip.
Recommend printing in ABS or ASA. Support the clip as indicated in the 2nd or 3rd screenshot. Preferred orientation is on a 45 by reducing the X-Y Separation setting from 80% to something that can print for you. I used 25%. (https://help.prusa3d.com/article/support-material_1698#xy-separation-between-an-object-and-its-support) . If you don't have any luck, print with the U shape on the XY plane. The tabs should still be strong enough even with layer lines.
Use a small file to sharpen the clip tabs and remove any elephant's foot around the base.
The author hasn't provided the model origin yet.