Does it have to be the same app for both platforms? If not, I'd recommend checking out Microsoft's RDP protocol and their own software that uses it (sorry, can't remember what it's called, maybe Remote Desktop something?).
Unlike most screen share protocols, it's not just sending pixels but abstracted window layout information (think XML but Microsoft-made). This makes the remote experience muuuuch smoother than pixel streaming, even on high speed connections but especially on lower bandwidth devices.
When Teamviewer started blocking connections because of exceeding the limits, I switched to https://www.helpwire.app/ which runs smoothly on both Windows and Mac. And it's free.
lax4ever
I have not used it personally, but I hear good things about Rust Desk
https://rustdesk.com/
Unlike most screen share protocols, it's not just sending pixels but abstracted window layout information (think XML but Microsoft-made). This makes the remote experience muuuuch smoother than pixel streaming, even on high speed connections but especially on lower bandwidth devices.
https://en.wikipedia.org/wiki/Remote_Desktop_Protocol?wprov=...