When I was younger and started singing Folk songs, also in public, I sang from my memory, never a textbook or anything like that.
Then friends and me were asked to do a gig over several hours (a wedding of friends) and we had to put up a hugh song and gig list.
I think, it was then when I had to use my textbook / printed sheets with the words on it.
During the last years I did not have the chance to perform in front of audience very much, but became quite less self assured.
Also, funny enough, I know the melodies of several hundred songs and mostly one or two verses including the refrain and I have no idea why I cannot memorize the complete song which I find rather annoying.
So I use to have a sheet in front of me but only look down if I ran out of words.
Which also means that I have eye contact with the audience most of the time.

There are so many things which fill up my brains and memories at the moment that I cannot keep all these words in my memory. Have not find a way to change this so far and simply do not know how to get a better memory.
A memory just for song lyrics would be great...