Ljubljana/Lake Bled, Tallinn or Budapest? September/October

I'm planning for a trip of about 5 days roughly that I can fit in end of September/early October. These three destinations are places I have never been before - I am very much into history and interesting architecture, museums etc, which is why I thought Budapest or Tallinn would be good options.

I was originally planning Italy (Rome or Bologna), but I think it would be way too crowded and as I've visited Italy before (only Florence), I wanted to get out of my comfort zone.

I am also really interested in nature and hiking, and I know Slovenia has a lot to offer. I know that it is possible to get from Ljubljana to Lake Bled & Bohinj, which both look amazing. (I don't drive so would have to take the bus or train.) Hoping that the weather would be reasonably good at the end of September?

I am still quite drawn to Budapest as I did want to visit the opera house, see Buda castle, the Parliament building etc. I don't really drink or party though, so I'm not super into city nightlife. Also Tallinn looks gorgeous, I know the old Town is beautiful, and it's also quite a green city I think? I do really like Nordic countries - I have previously visited Stockholm and really enjoyed it.

Overall I am leaning towards Slovenia - I would plan to stay in Ljubljana briefly and then move to Lake Bled/Bohinj for a bit. Also would be so cool to visit Triglav National Park. I have heard it's very safe for solo female travellers so that's definitely a huge positive. I am a bit nervous because I haven't visited central Europe as much as Southern Europe (my most frequent stays have been Portugal/Spain), so it's more new to me.