There are so many resources for writers today you simply need to use your favorite search tool to discover them. But for some mainstream options check out what's on this page.
If you want to recommend better or additional resources and research sites, make suggestions in the member forum.
Grammar & Styles
The Elements of Style by William Strunk, Jr. https://www.bartleby.com/141/index.html
Grammar Girl by Mignon Fogarty https://www.quickanddirtytips.com/grammar-girl/
Properly Capitalize a Title https://capitalizemytitle.com/
Grammarly - Grammarly is an American cloud-based typing assistant. It reviews spelling, grammar, punctuation, clarity, engagement, and delivery mistakes in English texts, detects plagiarism, and suggests replacements for the identified errors. It also allows users to customize their style, tone, and context-specific language.Wikipedia
Self-Publishing & Blogging
Amazon Vella (for serials)