After trying different tools to export messages from a slack workspace I finally found one that did all I needed, without errors and in a reasonable time:

slack-exporter

slack-exporter -c ./config.yaml

Configuration

SlackToken: <TOKEN>
RequestDelay: 1200
ChannelTypes:
  - "public_channel"
  - "private_channel"
  - "mpim"
  - "im"
ExportBasePath: "./export"
SplitMessages: false
ArchiveData: true
DownloadFiles: true
IncludeChannel:
  - "random"
  - "@goliatone"