Based solely on Google's announcement, after January 2024, the Basic HTML view will no longer be available and Google will redirect users to the default view of gmail.com that matches their platform and browser settings (see table below).
I haven't found information indicating what Google's intentions are for the Older Version of the Mobile view, however, as helpfully pointed out by @user1686, it is a distinct view from Basic HTML, so presumably it is safe for now and continuing to use that (or switching to it) may be a good option for you.

The Older Version of the Mobile view is significantly more limited (or "lighter" depending on your perspective) than the Basic HTML view they are retiring.
Keeping it may reflect the reality that, at this time, there remains a need for a feature-limited view of Gmail, and its simplicity fits the bill far better than the Basic HTML version which is loaded with features, and actually far from "basic."
Gmail Views
There are currently four browser-based views for Gmail. Two are intended for mobile browsers and two are intended for desktop browsers.
- Standard Desktop
- Basic HTML Desktop (Unavailable after Jan. 2024)
- Mobile
- Older Version Mobile
Google resolves the same link to completely different Gmail views depending on a user's platform and browser settings.
For example, the table below lists which Gmail view a particular link will resolve to based on the user's platform (desktop vs. mobile) and the browser mode (desktop vs. mobile):
URL |
Mobile Browser |
Desktop Mode * Mobile Browser |
Desktop Browser |
Mobile Mode* Desktop Browser |
gmail.com |
Mobile |
Mobile |
Standard |
Mobile |
m.gmail.com |
Mobile |
Mobile |
Older Version (Mobile) |
Mobile |
mail.google.com/mail/x/ |
Mobile |
Older Version (Mobile) |
Older Version (Mobile) |
Mobile |
mail.google.com/mail/h/ |
Basic HTML |
Basic HTML |
Basic HTML |
Basic HTML |
- Desktop Mode refers to the web browser setting, not the link labeled "Desktop" in the Mobile version of Gmail (which links to Basic HTML Desktop).
- Mobile Mode refers to using Device Mode in Chrome DevTools to simulate a mobile device. Chrome for Developers > Simulate mobile devices with Device Mode
- Older Version (Mobile) can be accessed in from a mobile browser without switching to desktop mode using a link to Older Version located at the bottom of the hamburger menu

