This allows you to block certain versions from logging into your server, every Minecraft version has a special number assigned to it called a Protocol Version. You can view a list of them here and find a generator here. For example, if you wanted to block 1.10 Minecraft you can see from that list that the number is 210. You would then change your config to,
block-protocols: , you can then add as many protocols as required separated by a comma if you wish to block more.
block-versions- default:  (String List)
This allows you to block certain versions from logging into your server, it is similar to block-protocols but allows you to use version names like "1.17" or "<1.17". For example ["<1.17"] would block allow versions less than 1.17. The less than operator and greater than operator are both supported for these versions.
block-disconnect-msg - default: "You are using an unsupported Minecraft version!" (String)