In the Scale Modelling Thread in the Miscellaneous and Personal forum, I’ve been able to submit posts with photos and never got that pop-up, and posted all my photos totally fine. Pretty sure I didn’t do anything different than what I always did. Something changed?
There was a recent update, so maybe.
Nothing in the What’s New specifically addresses this.
Are you by any chance trying to upload your photos directly to Discourse? Because that was never allowed, although at one time physically possible. You need to use a third party image hosting site like Imgur.
It looks like in the Scale Modeling thread that you were linking to IMGUR. That should be fine, although your images will no longer be visible in some countries due to recent law changes.
If you are getting the pop-up for embedded media, then the system thinks you are trying to upload images to the SDMB, not link to them. Depending on what device and software you are using, there may be a change there that is trying to upload the photo instead of trying to upload a link to it.
Was using imgur links to successfully post images in the scale modelling thread before.
Maybe this Canadian might have to consider that.
Are you in Canada? Imgur works fine in Canada and all other countries AFAIK except the UK, for silly legal reasons.
Oddly enough I was able to recently post an imgur link in a Pit thread, so I’ve had luck in some places. 
Weird. It should be the same everywhere.