Discord sharding is probably not effective at reducing memory usage - if anything, it will increase memory usage.
Enmap is by default storing everything in memory. You can change the fetchAll option to false to instead keep the data on disk, which will be a little slower, but it will take less memory. See: https://enmap.evie.dev/usage/fetchall
Generally, if you’re doing more, you will use up some resource more, and these techniques just trade one resource for another. Discord Sharding allows you to add more guilds beyond Discord’s limits, but it costs memory and CPU. Enmap fetchAll: false gives you some memory, but it costs disk space and your bot’s responses may be a little slower.
Hope this helps,