Why on earth this hasn't been updated to just permanently hide the assistant menu instead of it re-appearing after reboot is beyond me. Don't know why they messed with this feature to begin with. Just put single tap back to where it was initially or someplace else that does not involve this annoying assistant menu.
Yes it is something that happened to all galaxy s8 devices after the update, i did not notice till i read your post i am not really sure whether its intentional or not but probably it is like you said; some Apple style update BS.
Tap phone, settings, answering and ending call, select press volume up to answer. I don't have good dexterity due to arthritis so I was pretty upset about swiping due to the pressure needed to swipe. I have to use two hands just to answer using the volume up button. Hope Android/Samsung realizes this is a huge mistake for a lot of consumers.
So i found out that enjoy such"Luxury" of having a single press instead of swiping to answer and end calls i have to enable the floating assistant menu then use that "Luxury" feature THANKS alot samsung next time i am buying a true andriod phone that do not do that Apple style BS.
I just switched to the Galaxy S10+ and I noticed the feature is nowhere to be found, so it must be deeply tied into One UI. Let's hope Samsung puts it back in a following update.
Go to Settings > Accessibility > Interaction and dexterity > Assistant menu > Enable it, then scroll down to "Single tap to swipe" and Enable it. The annoying part is now you have the assistant menu floating around on all screens. But you can take the transparency to zero and make the menu size small.
Making compromises is for Apple users not us this is not acceptable by any means, was gonna buy the Galaxy s10 but now i will find another android phone that do not do such Apple, and yea i don't really care about people saying you will switch to another mobile for such silly thing cause i will cause i am the one paying 1000$ for the mobile i don't get it for free and such feature matter to me even if it doesn't matter to anyone idc, that's really it for me if they do not fix it the next update as a long time Samsung user the S4 then Note 4 then the S8.