First figure out which theme you are using. List installed themes via:
% pelican-themes -l
simple
notmyidea
pelicanconf.py does not set a THEME, therfore defaulting to notmyidea.
The template locaions are (update your python version as appropriate):
cd venv/lib/python3.13/site-packages/pelican/themes/notmyidea/templates
At a minimum a theme must contain these files, which could be altered in your local copy of the theme.
└── templates
├── archives.html // to display archives
├── period_archives.html // to display time-period archives
├── article.html // processed for each article
├── author.html // processed for each author
├── authors.html // must list all the authors
├── categories.html // must list all the categories
├── category.html // processed for each category
├── index.html // the index (list all the articles)
├── page.html // processed for each page
├── tag.html // processed for each tag
└── tags.html // must list all the tags. Can be a tag cloud.