The Salesforce Documentation states that URL Rewriting is not supported in Lightning Communities:
Is URL rewriting for creating custom vanity URLs supported?
No, URL rewriting isn’t supported for template-based communities.
In a Visualforce community we would use an URLRewiriter to translate friendly URLs that are useful for SEO into parametrized URLs that are useful for development. For example:
/category1/subcategory1 -> /customCategoryCommunityPage?category=123&subcategory=456
It is possible to do something for some detail pages:
However, that only addresses detail pages.
Are Friendly URLs possible at all in Lightning Communities? If not, what, if anything, can be done?