Noted! For others on Linux, the command to do the above would be: tar --zstd -cvf gossip-db-backup.tar.zst .local/share/gossip/lmdb
zstd compression is definitely worth it; gzip compression for my LMDB directory produced a file 362 MB in size and took 1.6 minutes. zstd produced an archive 49 MB in size and took only 10 seconds.
I also experimented with xz compression; that produced an archive 37 MB in size, but that took over 4 minutes to compress.