To gain root access you have to flash an optional zip file [0] after flashing LineageOS itself and the also optional OpenGapps [1]. If you don't do that, your Boxer app should pass these SafetyNet checks [2].

If you want both root and still full access to these SafetyNet-"protected" apps, you can try the alternative rooting solution Magisk [3] which specializes on bypassing these (imho arbitrary) restrictions.

[0] https://download.lineageos.org/extras

[1] http://opengapps.org/

[2] https://www.lineageos.org/Safetynet/

[3] https://forum.xda-developers.com/apps/magisk/official-magisk...

My bank app refused to install on a rooted phone. I used Magisk Manager to work around that. I guess it could work in this case as well. There is a 'hide root' option (or something similar).