If you've set up a fresh install of WordPress through Docker (https://hub.docker.com/_/wordpress/), one of the first problems you might run in to is if you try uploading a plugin or image that exceeds the default memory limit.
To fix this you can create an uploads.ini file in the same directory as your docker-compose.yml file with the following contents:
file_uploads = On upload_max_filesize = 256M post_max_size = 256M
Then in your docker-compose.yml file you should add the following:
services: wordpress: ... volumes: ... - ./uploads.ini:/usr/local/etc/php/conf.d/uploads.ini
Your compose file might be structured a little differently but essentially you just want to map your custom uploads.ini file to the default uploads.ini file provided by WordPress.
Restart your container then you should be good to go!