I don't think I am experiencing rumination because I'm not thinking about things I am especially worried about. Instead it seems that these things are tendentially problems that involve uncertainty and complexity.
It's as if my brain has difficulty being spontaneous and wants to analyse the problem to come up with a solution. It analyzes and searches for solutions, has difficulty concluding the search, then becomes tired and unable to make any progress. I then give up and decide to think about it the next day, but the next day it's as if a good portion of the memory containing the progress has been wiped and I have to redo much of the work. The end result is an often absurd inability to get things done. It can take me months to make a decision to see a dentist, buy something for my bike, buy train tickets, make up my mind about many things.
If I haven't made up my mind, I can't act. Or it feels that way. I'm not always so inhibited, but often.
I believed this was executive dysfunction, but I've been told that I have no executive dysfunction, at least on the particular test performed.
I see this discussion has largely focused on decisions and choices. For me that is less of a problem and the issues you detail here for me are generally related to any cognitive processes.
For example if I were to try to read a piece of text that has some complexity involved that I used to be able to understand without a single problem, say someone sort of argument with more than one logical step but certainly not a complicated argument or even a very simple logical statement from something as basic as my own bachelor thesis (in fact I cannot understand any sentence that involves any logical complexity even if it was written by myself when I was healthy) then I simply cannot understand these things at all, no matter how much time I am given.
It’s as if my head can’t wrap itself around more complex cognitive problems, no matter what time it is given and just starts going into hopeless loops that lead nowhere, rethinking something without being able to wrap itself around anything sensible at all.
So it’s certainly not an executive dysfunction problem for me, it’s a more general problem of cognitive dysfunction.
This sometimes reminds me of people with dementia that perform things in repetition and where thoughts are clearly following some sort of loops for which there is 0 reason (something like a dementia patient getting out of bed to put on their shoes to go back into bed, being told there is no reason to wear shoes in bed, only for this process to be repeated 10 minutes later again and over and over again).
This feeling off my brain going in loops, is something I had rarely experienced in my previous life before, however on the extremely rare occasion when this was the case (maybe somewhere around twice a year) it was always because I had spent the entire day working on some very complex logical problem for 10+ hours (or multiple days/weeks/months) and my head was trying to resolve this problem, even though I wasn't actively working on it anymore (it would lead to a terrible and interrupted sleep in which these loops of thoughts would continue even if they made 0 sense, luckily in the next morning my brain would be fresh again and I could tackle the problem with a fresh perspective/mind).
It's as if I'm purely lacking "brain power" nowadays.
Edit: I just saw this is very similar to what
@poetinsf described above and I can relate to everything that was said there.