Publish directly from LR Classic to Instagram

And see this article on how to post multiple photos with landscape & portrait orientations.

With all due respect, I do not think posting to Instagram is time consuming and convoluted. You export the photos to your hard disk somewhere, open up your web browser, navigate to Instagram and then in Instagram click on the plus sign to add photos, and then you select them from your hard disk.

The Lr/Instagram website is still up, with contact information. You might send them a message asking if they have made any progress in making their plug-in work again. The website does call it an “unofficial” plug-in.

…posting to Instagram has become a convoluted and tim-consuming process

By @johnb85879550

Even without a direct upload from Lightroom Classic, it can be relatively simple. Two ideas, if you haven’t already used them:

Idea 1:

Simply add the image to a Collection that is synced to Lightroom Photos in the cloud. Then all you have to do is select the same synced image in Lightroom on your phone or tablet, tap Share, and select Instagram. It will then ask you whether you want to create a Post, Story, or Message, and you’ll be on your way.

Idea 2:

Create an export preset that generates a copy with your edits (such as a JPEG), and enable the Add To This Catalog option. The preset lets you export with specific settings in one step, and the image appears in the Added by Previous Export automatic collection. The point of this is that if you are signed into Instagram in your web browser and click Create, a window opens where you can drag and drop images. So for example, if you want to upload an image, you would choose File > Export with Preset > [name of the preset], then select that exported image in Added to Preview Export, and drag and drop it into the Create window in the web browser. (Drag and drop from Lightroom Classic may not work in Windows; if so, in the Export dialog box also enable Show in Explorer in the After Export menu in the Post-Processing section so that the new export is revealed on the desktop, then you can drop that into Instagram in the web browser.)

All of that may seem convoluted at first, but the payoff is that after one-time setup, Idea 1 is just two steps: Sync to cloud, then share to Instagram from mobile device. Idea 2 is also just three steps after setup: Export with preset, click Create in your Instagram account in a web browser, then drag and drop into Instagram.

It's not Adobe's fault - Instagram prevents it.