Here are a few of the Author/Writer Facebook groups I belong to, in no particular order. Be aware that each group has its own rules and guidelines that you are expected to follow. Ignore or forget the guidelines and don’t be surprised if you get banned from the group.
There are plenty of other author / writer groups on Facebook. Memoirs are one group that you may not find many groups as memoirs by non-famous people tend to be a hard-sell.
Author Like a Boss: https://www.facebook.com/groups/authorlab/
Science Fiction, Fantasy, & Horror Authors, Artists, & Fans: https://www.facebook.com/groups/407560729441747/
Sci-Fi and Fantasy Art and Graphics: https://www.facebook.com/groups/1863911737194881/
Writing Prompts Group: https://www.facebook.com/groups/WritingPromptsGroup/
Authors and Creators Making Money Selling Books: https://www.facebook.com/groups/743617402482919/
Authors and Writers Helping Each Other Grow: https://www.facebook.com/groups/1976793849262471/
Writers and Authors Promotions: https://www.facebook.com/groups/writersauthorspromo/
The International Indie Author: https://www.facebook.com/groups/441469159372773/
Indie Books Promotion!: https://www.facebook.com/groups/490005547676565/
Writers Helping Writers: https://www.facebook.com/groups/27659251025/
LitRing VIP Readers: https://www.facebook.com/groups/1819874601609959/
Fantasy Writers Support Group: https://www.facebook.com/groups/1800355053523765/
Writing Bad: https://www.facebook.com/groups/1610163342625796/
Ninja Writers: https://www.facebook.com/groups/1582424518747057/
SPF Community: https://www.facebook.com/groups/1584291371854759/ – Self-Publishing Formula (SPF)
The Writer’s Workout: https://www.facebook.com/groups/1427053020895063/
Fantasy-Faction – Fantasy Book Discussion: https://www.facebook.com/groups/1378245525817971/
Inner Circle Writers’ Group: https://www.facebook.com/groups/1102819623195114/
Authority Self-Publishing: https://www.facebook.com/groups/821811664605563/
20BooksTo50K®: https://www.facebook.com/groups/781495321956934/