I agree that it is good for kids to be bored sometimes. This is when they use their imaginations. Get him to invent a game to play - you’ll play it with him. Suggest he look for a different way to play with existing toys. Find a new tv show for him to watch (maybe look up something from your childhood and tell him that mummy watched it when she was a little girl).
other ideas for more structured plans:
Board games (don’t be afraid to go for something with an older age on it if you have the patience to teach him the rules. My youngest started playing “Ticket to Ride” at around 6 and he loved it, even if he needed help!)
Colouring
Arts & crafts
dot to dots
reading
watch a film (set up like a home cinema with lights off, popcorn, etc)
Paddling pool
just playing in the garden
Walk to a different local park each day
museum
swimming
cinema
Lego afternoon (set a challenge to make something)
baking together
he chooses dinner and you teach him the whole process - he writes out a shopping list, go to the shop and he finds the items on the list, help him to prepare and cook the meal, teach him how to serve it up)
chores day once a week - my word 6 year old loved cleaning the toilet at that age (admittedly he’d use a ridiculous amount of cleaning spray but at least he wanted to help)
make ice lollies
make chocolates
local walks
if he likes Pokemon, download Pokemon go on your phone and go for a walk together catching Pokemon
beach/reservoir/lake/river/woods walks
if there are activities he really enjoys do them again!
have fun!