(Arq developer here) Haven't gotten many requests for it at all over the years. I presume it's because there are so many free options for Linux.

If it's open-source, Linux support is only a few hours with Claude away.

If it's not open-source, but the protocol is documented, see above.

If it's not open-source, and the protocol isn't documented, well... that makes the decision easy, doesn't it?