N++ currently actively rejects any non-ASCII chars for the user defined matched-pairs. So only char-codes 0-127 are accepted (and as the 127 is the DEL, in fact 0-126, so the ‘~’ is the last one)

IDK if this is a holdover from the N++ distant non-unicode past or there is a deeper reason. If you will opt to search an existing / create new N++ GitHub issue for it, here are the proofs of such rejections for the possible issue:

https://github.com/notepad-plus-plus/notepad-plus-plus/blob/a1aa8682d1cb8ac7e92b8eb98a4fc995d8d730ce/PowerEditor/src/Parameters.cpp#L5848
https://github.com/notepad-plus-plus/notepad-plus-plus/blob/a1aa8682d1cb8ac7e92b8eb98a4fc995d8d730ce/PowerEditor/src/Parameters.cpp#L5854

0x80 == 128
https://github.com/notepad-plus-plus/notepad-plus-plus/blob/a1aa8682d1cb8ac7e92b8eb98a4fc995d8d730ce/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp#L4654
https://github.com/notepad-plus-plus/notepad-plus-plus/blob/a1aa8682d1cb8ac7e92b8eb98a4fc995d8d730ce/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp#L4659
https://github.com/notepad-plus-plus/notepad-plus-plus/blob/a1aa8682d1cb8ac7e92b8eb98a4fc995d8d730ce/PowerEditor/src/WinControls/Preference/preferenceDlg.cpp#L4664