app screen overlay and annoying voicemail notification

hi
wonder if anyone can help with a couple of issues on my s7 edge
finally got it set up and working like a dream...but i've come across a couple of little things
firstly since i updated about a week ago i keep getting "screen app overly" which prompts me to go into settings etc the only way i've found how to fix this though only temporary is to toggle off everything then give new app permission this is annoying as it stops some apps from working which means i have to uninstall then...

app screen overlay and annoying voicemail notification

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