First things first, nothing is truly unsolvable. Proof of work and its energy consumption, for example, seems highly problematic to me but it would certainly no

First things first, nothing is truly unsolvable. Proof of work and its energy consumption, for example, seems highly problematic to me but it would certainly not be impossible to swap out the entire consensus algorithm for something else. Whether Bitcoin would still be Bitcoin in that case then becomes somewhat of a philosophical question. If you think it would still be Bitcoin, then that is not an unsolvable problem assuming you believe proof of work is not going to be a long-term viable consensus strategy. If on the other hand you think proof of work is a defining feature of Bitcoin, then that would be an unsolvable problem. With that out of the way, the major problems seem to be scalability, pseudonymity instead of anonymity, missing regulatory oversight, mining centralization, adoption and as already mentioned proof of work and its energy inefficiency. I am probably missing things, I went from really excited about Bitcoin to a more rational and pragmatic view about the time it reached dollar parity and haven't followed the development too closely ever since because in my opinion everything in existence is really far away from prime time and it will take some more new ideas on the level of Bitcoin itself to get there, i.e. some tweaks here and there alone will not be good enough. Also note that I mentioned such general things like adoption as problems but what I really mean there is in the interaction, for example between regulatory oversight and adoption. But I don't want to flesh those arguments out in a comment, it would just be very time consuming and I don't think I would have to add much if anything new, many others have discussed all kinds of problems again and again. Some will follow those arguments, some will dismiss them and repeating them once again won't change that.