Dear raina_b22,
I have the same symptoms. Restarting Bluetooth, WiFi, and Sidecar on both the Mac and iPad don't help.
The problem occurs with the Magic Keyboard 2 paired with the iPad and controlling the Mac through Sidecar.
I have a second Magic Keyboard 2 that's paired directly with the Mac. There are no Sidecar crashes when I use this keyboard that's paired to the Mac.
Besides Cmd-B and Cmd-I, there are some other key combinations instantly and consistently cause Sidecar to crash (with the keyboard paired to the iPad and using Sidecar):
- Escape key (very commonly key used to dismiss dialog windows)
- Command-minus or Command-plus (used to increase or decrease font size)
Devices in use:
1) 2018 iPad Pro 12.9" 3rd Gen (ipad8,5)
iPadOS 14.2 Beta 4 (this Sidecar crash has occurred since the public release of iPadOS 14.1)
2) 2018 Mac Mini
macOS 10.15.7 Catalina
Here are some other users who face this same issue:
https://old.reddit.com/r/iPadPro/comments/hk2kkz/sidecar_crashes_with_bold_and_underline/