Differrent Boards in IDE

I am trying to use an Arduino UNO to talk to an ATTINY via I2C. My problem isn't the software as such, but switching between UNO and ATTINY.
The problem being that if I have both projects open in the IDE and select UNO in board manager, then the ATTINY project also changes to UNO, and vice versa. This wouldn't be so bad if it didnt cause a compile error after changing if I have both projects open in the IDE. I guess this would work OK in VSCode, but I haven't tried, or how about V2.0 does this allow for multiple boards in the same instance of the IDE.
Any suggestions please.

You can open two instances of the IDE. This is one way: double-click your attiny ino file in your file browser and double-click your uno ino file in your file browser.

Just do not open both from the same instance of the IDE.

Yes, Arduino IDE 2.x does. However, you should be aware that Arduino IDE 2.x is still in the beta development phase, with lots of missing features and bugs. Assistance with the beta testing, is very much welcome, but if you only want a stable IDE for your normal usage, then I recommend using Arduino IDE 1.8.15 with the technique sterretje shared.

Thanks Sterretje,
absolutely obvious when I stopped to think about it, clearly my brain hasnt woken up yet!!. Really appreciate your rapid response.
Also thank you Pert. Think I will try V2 out, but not on a main project just yet.
Amazing to get such a quick response!