There is a zmk pull request open that adds split encoder support. If you use that to build your firmware if should work.
To be honest I have not tried it with this board so technically one scrollwheel is not working right now. Though I’ll change that soon. I used a fork that supports split encoder with zmk on my sofle and it worked, so you could use this config for some inspiration (here: github.com/dnlbauer/sofle-zmk-config).