GH page builds locally but online I get 404 for each post

If I run jekyll in my local git /docs repo dir it builds with bundle exec jekyll serve and looks OK using http://127.0.0.1:4000/docs/.

But if I try to go online to https://thebigbear.github.io I only get my posts showing, but clicking on any I get a 404?

Any idea? Is it something in my _config.yml file:

# Welcome to Jekyll!
#
# This config file is meant for settings that affect your whole blog, values
# which you are expected to set up once and rarely edit after that. If you find
# yourself editing this file very often, consider using Jekyll's data files
# feature for the data you need to update frequently.
#
# For technical reasons, this file is *NOT* reloaded automatically when you use
# 'bundle exec jekyll serve'. If you change this file, please restart the server process.
#
# If you need help with YAML syntax, here are some quick references for you:
# https://learn-the-web.algonquindesign.ca/topics/markdown-yaml-cheat-sheet/#yaml
# https://learnxinyminutes.com/docs/yaml/
#
# Site settings
# These are used to personalize your new site. If you look in the HTML files,
# you will see them accessed via {{ site.title }}, {{ site.email }}, and so on.
# You can create any custom variable you would like, and they will be accessible
# in the templates via {{ site.myvariable }}.

title: TheBigBear doclets
email: thebigbear@users.noreply.github.com
description: >- # this means to ignore newlines until "baseurl:"
  This is a collection of some of 'TheBigBear's blog posts.
baseurl: "/docs" # the subpath of your site, e.g. /blog
#domain: "thebigbear.gihub.io"
url: "https://thebigbear.github.io" # the base hostname & protocol for your site, e.g. http://example.com
twitter_username: TheBigBearUK
github_username:  TheBigBear

# Build settings
theme: minima
plugins:
  - jekyll-feed

# Exclude from processing.
# The following items will not be processed, by default.
# Any item listed under the `exclude:` key here will be automatically added to
# the internal "default list".
#
# Excluded items can be processed by explicitly listing the directories or
# their entries' file path in the `include:` list.
#
# exclude:
#   - .sass-cache/
#   - .jekyll-cache/
#   - gemfiles/
#   - Gemfile
#   - Gemfile.lock
#   - node_modules/
#   - vendor/bundle/
#   - vendor/cache/
#   - vendor/gems/
#   - vendor/ruby/

Please provide access to your source code so issue can be inspected.