In the bottom lists the final version for copy.

-d:release --opt:size -d:strip -d:lto

ref https://nim-lang.org/faq.html — Which option to use for the smallest executable?

Also (if CC is gcc):

--passC:"-fomit-frame-pointer -fno-strict-aliasing -ffunction-sections -fdata-sections -fshort-enums"

--passL:"-Wl,--gc-sections"

ref https://wiki.wxwidgets.org/Reducing_Executable_Size

• if no multi-thread needed
• if no exception handle needed
• if no runtime checks required

Then

strip --remove-section=.comment --remove-section=.note xxx

may helps reduce hundred Kb

• if some memory leak is tolerable