How to port Buffer.from() to deno2

Rewriting a webapp so that it can run in both Node or Deno2, I get stuck on the following. The function has to read a base64 encoded gzip buffer containing a JSON string. This is the node implementation:

import zlib from 'node:zlib';

function from_base64_gzip(str){
  let buff = Buffer.from(str, 'base64');
  let json = zlib.unzipSync(buff).toString('utf-8');
  return JSON.parse(json);
}

However deno2 does not have the Buffer object, and atob() only seems to work for strings and not for binary data.

Is there an elegant way to rewrite this such that it will run both in node and deno (preferably without extra npm deps)?