I've added this to quasar.conf:

    boot: ["i18n", "axios", "buffer"],

And created a file buffer.js in the boot folder:

import { boot } from "quasar/wrappers"
import { Buffer } from "buffer"

export default boot(({ app }) => {
  app.config.globalProperties.$Buffer = Buffer
})

and hive-tx still throws this error:

vue-router.mjs:3472 ReferenceError: Buffer is not defined
    at node_modules/hive-tx/transactions/signTransaction.js 

Nothing is ever as easy as yarn add ... with javascript or so it seems to me.