My experiences is that text messages can be selected to view inline, but not others. PDFs and word documents need their specific apps.

In case my question wasn't clear, here is an image of an attachment in mac mail, and one in Thunderbird. Would prefer to just see the attachments. Maybe there's no way to make this look more like Mac Mail in 115 version (I'm still running High Sierra and that's as high as I can go). But if anyone has a workaround, let me know.

there is a hidden preference and a menu item linked to showing attachments inline. There is a menu entry that says show attachments inline. On windows this is on the View menu. I have never played in the apple universe, I refuse the apple tax, so I have no idea how apple menus at set out. This item shows graphics in a number of open formats like JPG, GIF and PNG.

The hidden preference introduced in V68 mail.inline_attachments.text can have it's value changed using the Config Editor from false to true to display text attachments. Most Dat files, TXT files and of course EML emails attached.

I just looked at the attachment type in the image. Thunderbird offers you to opportunity to view PDF files in a new tab. PDF file are neither images or text, they are binary application files. The extent of your options with regard to that type of file attachments is the afore mentioned new tab. It might have something to do with the risks associated with PDF files as they can contain malware. I do not know.