These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.55 s (backtrack: 0/20).

[ebuild     UD ] app-arch/zstd-1.5.7:0/1::gentoo [1.5.7-r1:0/1::gentoo] USE="lzma zlib -lz4 -static-libs -test (-verify-sig%)" 2378 KiB

Total: 1 package (1 downgrade), Size of downloads: 2378 KiB