I sympathise with you lonelyman . You got run over by a bus on assumptions . Not sure what country in Europe you are in but hope your not freezing to death over there ATM .
Your in here asking people's opinions about how you should move forward with making contact with someone you haven't seen in a long time . Well I seriously doubt there is anyone here with formal qualifications in the best way to go about that , very much including myself , but here's my opinion anyway .
About you , you have some health issues or at least had some . You also have had enough of being treated like a friend in relationships you had which you hoped would lead to romance .
About the lady . You've rediscovered her , but don't know what her circumstances are .

If I was in your position I would try to make physical contact with her , as in face to face . Now you could either just lob up to her work unannounced , or if you want a softer approach you could drop a letter off there ( hand written with one of those old fashioned pen things ) either way you just tell her the truth ......explaining that you came across her profile online , had been thinking about her and where hoping the two of you could catch up , be that for a coffee in the park , pizza on the beach or dust off your suit and an evening at a nice restaurant of your choice ( her choice ) .
So considering it's been 20 years and your hope is that you can meet her again for a meaningful relationship , it's a long shot huh , even the most optimistic person wouldn't give you high odds on it all falling into place , but if that's what you want to do then seize the day and do it . You may lack confidence ? , well just fake it . Be confident . What's the worst that can happen ? She tells you that she doesn't wish to see you ... well at that point you spread you hands , tilt your head and smile at her and say " well you can't blame me for trying , your not an easy lady to forget , you have my number . It's great to see that your doing ok and having a nice life . Maybe I'll see you again in 20 years ? , maybe I'll see you sooner if you wish "
Carpe diem ... one day we will all be dead and we will have lost those chances we were too afraid or shy to take .
Now on the subject of "should you keep trying if she sez No" no you shouldn't , you know that , you tried to explain earlier . I understand you didn't mean like being a stalker .
Good luck and don't die wondering . There's no shame in trying and failing at anything as long as you have tried .