Upstream has released updates that appears to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing
BungeeCord Changes:
6613aaea Add test fix for library classes being visible to non-dependent plugins
53ce6b93 #3200: Fix protocol for 21w40a
d8e29384 #2466: Use switch in "BungeeCord" plugin message handling
5cf869df #3198: Remove terminally deprecated SecurityManager
f26f7d88 Add optional 1.18 (21w40a) snapshot protocol support
