The symptoms you describe are only too familiar to people such as Henry and myself who are getting on a bit in years. They are also similar to the ones experienced by people with several other conditions including shock, PTSD, TIA & stroke, mild brain damage from blunt force trauma, as well as many side effects from certain drugs, which is possibly where the term chemo=brain originates. They are also some of the symptoms now being explored as part of the long-covid syndrome. Thus, you are not alone in 'suffering' with this condition. It is true that certain regular brain exercises can help to stop further deterioration. However, it might be useful to discuss your concerns with a doctor or pharmacist to see if there are any of your drugs that you could change to try to alleviate some of these symptoms.
My own 'brain exercises' are largely confined to writing rhyming verse, which helps distract me from dwelling on the many negatives in life. It is also an activity that gives great leeway in terms of loss of memory and deteriorating ability to problem-solve. Distraction is often extremely useful when trying to sort out difficulties with psychological 'stuff'.
I like Henry's concepts of a sense of humour and a modicum of acceptance but these are probably more appropriate to our age than yours. However, there was a little book I once read called 'Don't Sweat the Small Stuff' which, as I recall (badly), gave humorous quips about things in life that really should not occupy too much of our brain time for too long.
I do hope that you can find a way through to a satisfactory outcome on this issue.