Standard PCA works different, its one projection of your data to another coordinate system. Its not an iterative process having a non-close form to optimise, where you need a stress value. So, you don't have any stress value and it does not make sense to calculate one. On the other hand, you have other statistics after PCA, like explained variance.

Hi Matt,

Thanks for your response - that makes sense!

See these links:

https://rdrr.io/github/kadose/EASiP/man/pca.stress.html

https://cran.r-project.org/web/packages/ggfortify/vignettes/plot_pca.html

https://websites.pmc.ucsc.edu/~mclapham/Rtips/ordination.htm