Back when the SMS news hit, I was surprised to learn that the Signal (Android) client had vendor lock-in, in the sense that there was no official way to export all the data in a format that other programmes, or even humans, could read.
I found various third-party projects on Github that purported to be able to do this in some shape or form, but they were all brand new, experimental, incomplete, etc., and some of them looked very difficult (= error prone) to set up and use.

It's been a couple of months.

Is there an official way to export all Signal data now, including SMS/MMS, media and so on, or failing that, consensus on a proven method involving a somewhat matured third-party project?

Ideally I'd like to have

• a cleartext copy that I can use as a searchable archive, ideally in a format that'll render in a browser
• something that Google Messages can import on Android
• a custom output format that retains absolutely everything and can be re-imported into Signal in theory [this the official backup function should be able to do. I hope.]

Something that runs on Linux, or directly on Android, would be optimal.

How do you export your Signal data?