Nonbonded interactions on the GPU i'm using this command
gmx mdrun -deffnm nvt0 -nb gpu

but got
Nonbonded interactions on the GPU were requested with -nb gpu, but the GROMACS
binary has been built without GPU support. Either run without selecting GPU
options or recompile GROMACS with GPU support enabled

I've Nvidia rtx2060 with cuda 11.1 on ubnutu 18.4.5
As the error tells you: the GROMACS binary has been built without GPU support.
Did you install gromacs with apt-get? Usually these kind of programs are shipped with a basic built, with a lot of features disabled.
If you did built gromacs from source, then cuda was not found during configuration.
I would try building gromacs from source and:

be sure cuda is in your path and check that nvcc and the drivers have a matching version
run cmake and check the output, to see if the video card is recognised
run cmake with -DGMX_GPU=ON

Note that it seems that gromacs doesn't support multiple gpu accelerations( e.g. it is either openCL or cuda, you can't have both)