Kim19, that attitude to single women dining used to be common throughout, inc uk. i guess it stems from the suspicion that if a woman is dining alone then she is looking to pick up a man.
I have traveled alone to Europe several times. Lisbon is one of the places I like most because it’s safe, easy to get around by foot, many people speak English well, the climate is nice, they have excellent wine, and it's less costly compared with some big cities. Still, Portugal has other locations besides Lisbon that deserve attention, including Algarve, Porto, Cascais, Sintra, Obidos and Madeira. When visiting these areas, I like to explore alongside a local guide from gowithguide.com/portugal/guides
Have you thought about going with a group.? I'm on my own but have has two really good trips with Riviera Travel. One to Seville, Alhambra etc. The other to India. Lovely group and the tour mangers were fantastic.
Have read and heard that Paris is desperately down at heel at the moment. Have been a solo traveller for many years and have never encountered any problems in any city but I did experience an aversion to solo females dining in upmarket restaurants in Italy. Strange. Thought it was me but...happened more than once.