json -> gzip compress -> base64 -> data[] -> gzip decompress -> json

JsonCompressDecompress.cs

using System;
using System.IO;
using System.IO.Compression;
using System.Text;

// read json
var file = @"somedata.json";
using var inStream = File.OpenRead(file);

// compress
using var memStream = new MemoryStream();
using var outStream = new GZipStream(memStream, CompressionMode.Compress);
inStream.CopyTo(outStream);
outStream.Flush();

// convert to base64
var data = memStream.ToArray();
var base64 = Convert.ToBase64String(data);
var len = base64.Length;

// convert from base64
var indata = Convert.FromBase64String(base64);

// decompress
using var compressedStream = new MemoryStream(indata);
using var zipStream = new GZipStream(compressedStream, CompressionMode.Decompress);
using var resultStream = new MemoryStream();
            
zipStream.CopyTo(resultStream);
zipStream.Flush();

// conver to string
var outData = Encoding.UTF8.GetString(resultStream.ToArray());
            
Console.WriteLine(outData);