> Wish that I could use my iPad as a second screen.

No wishing necessary. Before apple sherlocked the idea with sidecar there have been multiple apps that let you do that and are (somewhat) cross-platform (Luna display, duet, ...). These apps are still around and much better than the apple one for specialized use cases like art, they cost money though.

Or, if you don't need high speed, just go the simple vnc route, e.g.

https://kbumsik.io/using-ipad-as-a-2nd-monitor-on-linux

There's definitely ways you can do that. Look into programs that use HDMI dummy plugs.

It's a little stub that plugs into an HDMI port trick the OS into rendering a separate screen. Then there are a lot of apps that let you display/interact with that virtual screen, usually through some kind of browser. Acts exactly like any monitor you plug in, regardless of OS.

It seems silly to need hardware for this, but it's a very clean/stable way to do this without mucking with config files or using weird hacks.

You don't even need dummy plugs with macOs now. You can use BetterDummy instead

Finally! I'll have to try that out.

Apparently u can do that on windows with something called Duet (see https://youtu.be/PIKB0sJg0_Ij - the video mentions another software ad well)

I use Deskreen to attach an Android tablet to my PC. All it requires is (I think) a modern browser for the mobile device (and you currently need an hdmi dummy plug on the PC).

Deskreen looks like the best solution out of all of the ones listed here.

while you're at it, get another Tesla for a second windscreen!