HN user
Using a DSLR as a webcam is pretty straightforward with other Linux distros: https://www.crackedthecode.co/how-to-use-your-dslr-as-a-webc...
I've been using this for ~2 years now, and it's been rock solid.
Same here, using an '89 Model M which I've modded to support native USB connectivity and also using QMK [0]. The ability to leverage all of the niceties of QMK (especially key remapping) combined with the feel of the Model M is what's kept it as my primary day-to-day keyboard some time now.
[0] https://www.crackedthecode.co/how-to-supercharge-your-ibm-mo...
I documented the process for using a DSLR as a webcam in Linux, and it does look like the A7III _should_ be supported:
https://www.crackedthecode.co/how-to-use-your-dslr-as-a-webc...
Author of the article here, thanks for the feedback! I've been using my DSLR as my daily-driver webcam for ~3 months now, and it's been working perfectly. Glad you found it helpful.