I personally was able to check the list of restricted apps for each mode (top panel, accessible when you click "Restrict apps" in the Modes settings. (For each mode please make this change)
I was able to, for example, visit the sleep mode settings and change the apps that it restricts.
Yes; Settings is erroneously included and selecting it in the bottom half list does nothing as expected. You gotta check the top panel for it by scrolling through it and hitting the little circular minus button on it.
Remember to always monkey around and tinker before you call something a bug.
I will admit this isn't completely clear and I had to draw on my prior experience to try and monkey around but was able to reliably find the restricted apps list for each mode and customize them; which *SHOULD* help you avoid this nasty softlock.
Samsung does need to patch it; Settings absolutely doesn't belong in the restricted lists like ever.
That being said; if you can edit your quick access bar in the notification shade, you should be able to throw Modes into that list and that gives you a quick escape toggle if you do softlock your Settings app behind Modes.
If you just add the modes toggle to your notification shade if the apps ever get stuck in restricted mode, just enable another mode using the notification shade and then disable and this seems to fix this issue every time.
