Hi Salim.
This is a good question and I can relate, as my original teacher was funded when I was younger by my dad. As time went by, that dried up and i found myself 10 years later with nothing official but a grade-2 qualification and some rusty fingers.
I took it upon myself recently to get a new teacher and had her assess me based on what I could play now (a few Chopin pieces and Clare de Lune) She said What I play is post grade 8, I was shocked.
Now I didn't need a teacher to enable me to physically play these pieces - why, because I loved playing them. I got parts incorrect over and over, i watched performances to understand how it should sound (not taking interpretation into account) and bought informative music that helped with some complex fingering. I probably took way longer to get there than had I had a teacher, and had I practiced correctly and consistently, but when becoming a professional pianist was clearly out of my scope, it's fair to say I lost some motivation.
What I would say is you can use logic, you have the internet at your hands, the only thing that holds you back is you. Within reason, yes don't expect to jump into Liszt pieces and play them perfectly, but you can hear pieces, you can read music you can physically know what is way out of your capability and what is maybe just outside... I would recommend taking that logic into account and play what you love to play, and keep pushing them boundaries.
You can, of course go down the totally opposite route and purchase the ABRSM books and work your way through the grades, whether you take the exams, or just prove it to yourself, they have the syllabus on the website that explains what is expected of you each exam, make yourself a mock exam, learn the pieces and see how you do, find your limit and keep pushing it.
I think the two things that make a teacher so invaluable is 1 - discipline. rather than hideaway from parts you struggle with, teachers bring you out your comfort zone and get you to play pieces that while you may not love, but will help you technically play the pieces you do enjoy at the end.
Two - Knowledge, If a person with degrees, qualifications and concert performances under their belt are telling you how to do something - they're telling you for a good reason! you can't easily obtain that 1-2-1 knowledge anywhere else. Think about what your end goal is with the piano and the time frame.
If you're setting yourself 50 years to play the hardest piece you've ever played, I believe you can push yourself, diary your progress, be logical with the way you learn without a teacher and still be satisfied with your own performance. I could go on and on, but i've probably lost your interest already!
Good luck. Feel free to message for more of my drivel!