Mixed Model in R with distance matrix, continuous variables, and categorical variables

I have a distance matrix that is constructed based on Bray-Curtis distances from microbiome data and metadata. My metadata has both categorical and numerical factors. I was thinking a mixed model would be a great way to see if one of the numerical covariates is significant after adjusting for the other covariates. However, I am open to other ideas. I hope that there is a package in R that can do this. I tried to work with GLMM-MiRKAT but it doesn't give me a p-value for each covariate.