The ornamental design for the extendable universal paint brush holder, as shown and described.
FIG. 1 is a front view and a rear view of the extendable universal paint brush holder;
FIG. 2 is a top view of the extendable universal paint brush holder;
FIG. 3 is a bottom view of the extendable universal paint brush holder;
FIG. 4 is a right side view and a left side view of the extendable universal paint brush holder; and,
FIG. 5 is an environmental perspective view of the extendable universal paint brush holder, the dashed lines showing the paint brush and the extension handle forming no part of the claimed design.