facetiously, lfog from long covid can explain some posts that laud natural immunity and, picking up an analogy, daily drinking as protection from alcohol effects.
To serious questions mentioned above:
vaccine after covid: some recommend one vaccine. Two doses work in tandem: immune system learns the pattern, and then applies it. So, disease works as one dose and second is beneficial. Both wane with time, may require a booster, testing for antibodies makes sense
antibodies are not an only source of protection, B/T-cells that are not easily measured provide protection even after antibodies fade, both after vaccine and after disease. Protection might grow with time.
vaccine decreases both infectivity and transmission, but to lesser degree than serious disease and decreases faster with time. If you consider a chain reaction, decreased transmission rate significantly decreases overall transmission. I am not hearing about prolonged transmission of several steps among vaccinated, it usually jumps from unvaxed to vaxed and then gets stopped soon.
look up what general health approaches are recommended for long covid. I am pretty sure it is not posting on YWN, most probably exercise.
Flu seems to be very low last year and this so far. you might be having something else or even repeated covid? this might explain constantly high antibody levels.