This post seems to describe the same issue, and like OP the suggested solution does not work as my right click context menu has no "Exclude" option in the explorer, and my explorer settings menu has no option to show all files.
After searching it seems this may be a missing feature from Rider. I am able to remove the node_modules from my index, but so far there seems to way to exclude the folder from search results, making the search feature not practical for me in our project. Search is important to my workflow and it seems this feature is present in WebStorm, but I cannot find a working solution for Rider after going through other posts requesting a solution to the same problem. I feel like I must be missing something, but the other posts seem to say the same: the index can be modified for the node_modules folder but it cannot be excluded from search