As a maintainer of devel/ikos, could you have a look at PR #252648:
In short, TBB version 2021 will soon be available as devel/onetbb but the port you maintain does not build correctly with it, see the following Poudriere run:
and error logs:
CMake Error at cmake/FindTBB.cmake:186 (file):
file failed to open for reading (No such file or directory):
Could you try to provide a patch (important: *by replying to this PR*) to facilitate the migration to devel/onetbb ?
To help you modifying your port, expected patches to devel/tbb and devel/onetbb are available in PR #252648.
Thanks for your contribution,
The upstream needs to fix this.