please look at the attached svg file :
i can make a hole in the big shape using the green one by selecting them both and menu -> path > difference
bu not with the winter symbol.
any idea on what's going on ?
It's probably because you have the snowflake inside a group (id=g4177), along with about 15 additional unused/useless groups also inside that group. Look at the XML below. Boolean operations such as Difference only work on paths, not groups.
The blue highlighted item is the snowflake path.
You can simply ungroup the snowflake and just delete all the useless groups from the XML. Then it will work fine.
Hint: to bring up the XLM Editor hit Shift+Ctrl+X
Alternatively, you could also use the Edit Paths by Nodes Tool to select only the two paths before applying the Difference operation, however that will just leave all those messy useless groups. So it's better to delete them.