BetterTouchTool Version: 4.203
PC keyboards have an "Insert" key which apparently equals the "Help" key that was present on older Mac keyboards. This key is useful when working with Windows and Linux through remote access software like Citrix Viewer, because Ctrl-Insert and Shift-Insert trigger the "Copy" and "Paste" operations, respectively, in a lot of contexts.
There is an old bug report which says that BTT does not properly support this key: Generating INSERT key
However, I was able to map "RControl-´" to "Insert" (and "Shift-RControl-´" to "Shift-Insert" etc.) successfully with BetterTouchTool 4.203, and this does work through Citrix Viewer. To record the target shortcuts which include the "Insert" key I simply connected a PC keyboard and pressed the combos there.
The only very minor and probably easy to fix quirk is that BTT shows the key as "?", even though as I said it functions well.
macOS 13.5.1 on MacBook Pro 14" M1 (2021)