How to check for compression?

I would like to understand if I am using compression (zstd, not zlib) in this way

to be honest I am finding this tool extremely confusing and actually I do not know if is even supported since the image is 4 months old meanwhile the zstd commit is also around 4 months old…

plus (after a huge research on where the cli binary is, since is not in the path for absurd reasons) I cant even print out the status or the configurations

Yes that is correct. You can verify it by checking this line in the backup log:

COMPRESSION_LEVEL Zstd compression is enabled (level: default)