Great ideas in this topic.

However, mnemonics are suggested over and again. I'm not very fond of mnemonics nor creating relationships between fictive objects (method of loci) unrelated to what you are trying to remember in order to support what you are trying to remember in the first place.

Instead, I would be very interested in hearing some strategies of how to reinforce the relationships within the actual topic being learned. By perhaps when trying to devote something to memory, consciously performing a mental routine. For example taking a mental photograph of yourself in front of your car with the appropriate background in order to remember where you parked your car. Or visualizing yourself dialing a phone number you want to remember. Mindmapping a new term with similar words as well as antonyms. Even better, pseudocode for putting something to memory.

What methods work for you?

I find this is frequently a big problem. Out of all the shortcomings I have, "not remembering" is probably the most disastrous for me.

For most of my life, I had assumed that this was something inherent about me. This led me to develop lots of tricks not for remembering, but for being good at not having to remember. I have thousands of text files stored on my computer's hard drive that I can search. When I started doing this, I'd never be able to find what I was after because I couldn't even recall a single keyword that would identify the right file for me. But over time I've gotten better at choosing smart ways of phrasing my notes, such that they're easier to search. Similarly for programming -- I carefully document even fairly trivial programs and try to keep a very strict folder hierarchy so that I'll be able to find what I need when I need. Sometimes I find useful programs that I can't even remember writing.

I now think that I was at least partially wrong in assuming that my memory cannot be fixed. I am looking forward to reading advice on this topic.

It sounds like you may benefit from a nootropic stack. Start with Piracetam/Choline/Sulbutiamine. Of course, if you aren't getting enough aerobic exercise, then fixing that will have a larger marginal benefit in terms of memory than any stack I know of.