There’s really nothing to it. If your WordPress site is setup right, all you need to do in the slider manager is insert the images into the slides. The theme saves your attachment ID’s and WordPress generates the URL’s to the attachments and saves them.
Honestly, I thought I was following the issue until you said this:
I’ve tried images from library and several different URL paths with http and without – even using the path to sample image from the Layout Builder templates. The image ALT tag is NOT displaying in the image box.
I’m a bit confused by this, as the theme’s slider manager does not allow you to put in any image paths. This is all done for you and you have no control over it. So, I’m not totally sure what you mean by this.
Unfortunately the problem you’re citing sounds pretty unique to something you’ve done. I can’t remember an issue like this with anyone else to give you any kind of general tips. I will need to see a link to the issue to really tell you anything substantial.
Just post the slider on some subpage that isn’t linked to from your main navigation and let me have a look.