In reviewing the output of make -n install, I notice certain paths are missing '/' separators: 

if test "x" != "x" ; then \
	rm -f /usr/local/python3.9.9/binpython3.9-32; \
	lipo  \
		-output /usr/local/python3.9.9/bin/python3.9-32 \
		/usr/local/python3.9.9/bin/python3.9; \
fi

There should be a '/' between bin and python3.9-32 and other lines have the same issue. The Makefile source lines where I see this error are:

        if test "x$(LIPO_32BIT_FLAGS)" != "x" ; then \
-->                rm -f $(DESTDIR)$(BINDIR)python$(VERSION)-32$(EXE); \
                lipo $(LIPO_32BIT_FLAGS) \
                        -output $(DESTDIR)$(BINDIR)/python$(VERSION)-32$(EXE) \
                        $(DESTDIR)$(BINDIR)/python$(VERSION)$(EXE); \
        fi
        if test "x$(LIPO_INTEL64_FLAGS)" != "x" ; then \
-->                rm -f $(DESTDIR)$(BINDIR)python$(VERSION)-intel64$(EXE); \
                lipo $(LIPO_INTEL64_FLAGS) \
                        -output $(DESTDIR)$(BINDIR)/python$(VERSION)-intel64$(EXE) \
                        $(DESTDIR)$(BINDIR)/python$(VERSION)$(EXE); \
        fi


I think the lines I've marked with --> above should have the '/' after $(BINDIR).... ????

This has been fixed in 3.11 with GH-28659, but the fix hasn't been backported due to the unlikelihood of this issue actually being a problem and a procedural wrinkle in the original PR.  I suspect a clean backport would be accepted, but this is still a rather low-priority issue.