Is there an opencv version 4.x package for the beaglebone black? I do not have enough room on my BBBlack to build opencv4 from source.
By "enough room" do you mean RAM, or do you mean eMMC (file system)?
If the latter, then using a large uSD card is probably part of the
solution. If the former, a large uSD card with a swap file defined /might/
be part of the solution.
Other than that, setting up a cross-build environment on a Linux box
might be feasible.