Ttgjyuk

Suppose a paper has authors A, B, C, and D. The first author, A, isn't in academia anymore, and much of my work is inspired by the senior author, D. I've also only communicated with author D.

Can I say/write "author D et al."?

When I looked this up, "first author et al." is the recommended version, but I would rather prefer to say "author D et al."

This isn't for a formal paper submission, but rather for something like a blog post describing my recent findings, which I hope will be published in the near future.

Your feelings and the journal citation rules might not align the way you want them to be. Therefore, I suggest you stick with the accepted norms and go with author a et al., even if it is an informal conversation or blog.

Using any author other than the first author in citation would not only do injustice to that author, but would also be a disservice to the readers. Readers would probably be confused when trying to find the bibliography of that citation in the reference list.

I think in an informal medium like a blog post, you could convey that author D is the main character in the “story” you are trying to tell while still maintaining proper citation standards by saying something like, “Author D and his/her colleagues (Author A, et al., 2018) have shown that...”

It just isn't that much work to name everyone. Think of all the work all the authors put into that paper. We can all afford to spend one extra second reading all of their names. And that extra second might make someone recognize the name on a file and result in someone getting a job they otherwise wouldn't have. There's no justification for using "et. al."

The only situation when this is common is if you're referring to multiple papers at once. However, even then you'd probably want to use formal citations in parentheses (like mentioned by LarrySnyder):

LAST AUTHOR et al. have done a lot of work showing phenomenon X (AUTHOR A et al., year; AUTHOR B et al., year).