As a resident of Ukraine and several times in Bulgaria, I assure you that there should not be problems with tourism in these countries in tourist and near tourist areas. And if you decide to travel to Ukraine - freely ask questions to me.
HI Aakanksha. I haven't been to those countries, I have been to Slovenia and Croatia and they were perfectly find and I hitchhiked. I would suggest going for it, but with appropriate planning about where to stay and taking proper precautions like not wandering around late at night.
Hey! I can assure anyone Romania & Bulgaria are very safe to travel to as a solo traveler. You asked about Ukraine too, but as I'm writing this answer in march 2022, we sadly all know it's a war zone.
In general, for solo female travelers it's better to go to big cities and take common sense precautions. With the help of locals and tourists I put together this very informative article: Is Bucharest safe? You cand read it here: https://deeajourney.com/is-bucharest-safe/ Romania and Bulgaria are both very beautiful when it comes to sightseeing. Also people are welcoming, food is delicious and prices are affordable. So don't miss out. :)
Moldova is similar to Romania - not just language but culture as well. I just came there (I am female solo traveler) and I felt super safe! You can read my blog about Moldova trip: https://chi-nese.com/is-moldova-safe-for-tourists-solo-female-traveler/
No why? That countries are also beautiful and suitabke for solo travelers. It is not like Egypt or Turkey. Only travel destinations in Romania and Bulgaria are kinda weak. In Ukraine thre are plenty of things to do and to see. For example u can visit Lviv and see this architecture. Or Lutsk where u can see the castle or urban town. Now thx to urban vision lutsk https://algorytm.ngo/en/projects/urban-vision-lutsk that city really becomes innovative. Or Kyiv. That is such a TOWN. So def worth to visit