RSS validation by w3.org fails

Describe the bug

The Feed Validatior at https://validator.w3.org/feed/check.cgi reports an issue for the RSS Feed:

• guid must be a full URL, unless isPermaLink attribute is false
• description should not contain HTML: p

There doesn't seem to be any way in the GUI to configure the RSS in a way that will make it pass the w3.org validation.

Relevant logs and/or screenshots

You can see the validation results of our podcast at https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fpodcast.internet-czas-dzialac.pl%2F%40icd%2Ffeed.xml

Context

• Castopod: 1.10.4
• OS: Yunohost
• Web server: Nginx