(Maybe it is a bit related to this: we just updated the macOS version on the openLCA website. A calculation library was missing.)
The memory usage depends on the calculation type (quick calculation, analysis, ...), the LCIA method, the number of processes in the system (product system > statistics) etc. but it should not be related to macOS. I did not tested the bottle example but a plain ecoinvent 3.6. product system without LCIA method and I could run a full analysis which does a full matrix inversion with ~ 4 GB of memory (it worked without changing the default settings):
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In the current version you can download additional libraries for sparse matrix calculations from the start page or via the preferences (Preferences > Configuration):
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These libraries only work for the quick calculation but then I could calculate the system with < 800 MB of memory usage:
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However, openLCA currently switches to dense matrices when you calculate LCIA results. So the memory usage is higher then (but should be still smaller when you use the quick calculation).