Long tale short, it depends, but likely yes unless reddit stops what it is doing.

Almost every post will contain experiences that could identify someone, so the wisest move would be to assume yes, or naively try to classify each post as 'bread-crumb' or 'not bread-crumb' for their specific processing then store and sell each separately. Non exhaustive list of personal data criteria:

• If the comments are tied to, or not stored separately from, your identifiers, (email, IP, handle, site ID, location, etc,) then yes
• If your comments are not anonymous or include details about you, then yes.
• If the data will be processed to identify you, then yes.
• If the data will be used to profile you, then yes.

Unique information about you, such as your subscribed sub-reddits, your browsing habits, the time spent on each link, your writing style, etc may also count as personal data if used to identify or target you.

https://gdpr-info.eu/art-4-gdpr/

(1) ‘personal data’ means any information relating to an identified or identifiable natural person (‘data subject’); an identifiable natural person is one who can be identified, directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person;

[...]

(4) ‘profiling’ means any form of automated processing of personal data consisting of the use of personal data to evaluate certain personal aspects relating to a natural person, in particular to analyse or predict aspects concerning that natural person’s performance at work, economic situation, health, personal preferences, interests, reliability, behaviour, location or movements;

(5) ‘pseudonymisation’ means the processing of personal data in such a manner that the personal data can no longer be attributed to a specific data subject without the use of additional information, provided that such additional information is kept separately and is subject to technical and organisational measures to ensure that the personal data are not attributed to an identified or identifiable natural person;

[...]

(15) ‘data concerning health’ means personal data related to the physical or mental health of a natural person, including the provision of health care services, which reveal information about his or her health status;--