Google killing off their basic HTML version of Gmail due to basic HTML not including 'full feature functionality' seems like code for 'we don't make ad revenue off this version'.

We relied on the basic HTML version while doing arctic fieldwork in 2017 using low bandwidth satellite internet. Gone were extraneous graphics and junk ads getting served - just mail. It's also no longer possible to auto sort messages in the full version without enabling tracking to serve ads.

https://www.theregister.com/2023/09/25/gmail_basic_html_discontinued/ 

 @7d839974 I understand your point, but as long as they don't cut mail client support, I am not bothered.