Created a new library in the Symbol Library Editor
Clicked in “Import symbol”.
Selected this new library.
Selected the MCU_Microchip_ATmega.lib file previously downloaded.
At this point I would expect to be able to select one of the symbols in the library (ATmega32U2 in my case). However, I get the ATmega64L-8AU, and its alias, imported.
How can I select the particular symbol I’m interested on?
The import function is not meant to import one symbol from a library but to import a previously exported symbol plus its aliases. (confusingly such exported files have the same file endings as normal libraries.)
To get a symbol from one lib to another both need to be in the same project.
I would suggest you add the downloaded lib to your projects symbol library table. (via preferences -> manage libraries found in the symbol editor)
On the left side of the symbol editor there is a tree view of the libs plus the symbols contained in them. Right click on the symbol you want to import into your personal lib -> copy.
Right click on the target library -> paste. Do the changes you want to make to the symbol and save the library. After that you can remove the library you downloaded from the symbol lib table.
The developers worked mostly on PCBnew the last years(?) and the mechanic underneath EEschema is a bit dated by now and not how they want it. At some point they will modify EEschema’s internal workings to be more in line with how PCBnew handles footprints… which means one symbol per file and a folder would be a library.
But that’s down the road. So yeah, probably not worth it to report as bug at the moment as it will change anyway.
IMHO.