Flu jabs can be planned ahead and can be based on the most common strains circulating each year. At the moment, the development of any covid vaccine is a reaction to any new strains and their speed of transmission, so I think any annual vaccine may not be quite ready yet.
As for a 4th jab, I've had 3 but being in the extremely vulnerable group I'll have a 4th (my booster) at the end of February.