He’s five, so his TV (and iPad and game console and...) time should be minimal and you still have the authority to simply cut it. Of course, there’s school work and remote lessons, but I see no reason why he should have unlimited access.
The next step for me would be to make sure that there’s a good selection of “material” available, ranging from his usual toys and books, but also including household items (blankets? a broomstick? a few boxes? a ball of string), crafts materials - and you can really use nearly everything down to (reasonably clean and safe) trash.
Then I would do nothing.
The inner impulse to do something, explore the available options and get creative is strong at that age. And boredom sparks creativity. Yes, we want our children to be active, we want to offer and suggest “good” activities, but if you want to encourage “creating” something vs. “consuming” something (TV, computer games), you need to let him develop his own ideas. This is also a valuable exercise in delayed gratification. Consider how computer games are designed to to trigger very frequent psychological rewards and how much effort it is in comparison to craft something before the gratification of having made something.
If your locale permits (considering the Covid rules and your environment), send or take him outside. At that age, kids need to just run around, jump, climb on things and generally move a lot. You can’t expect academic performance without physical exertion. There’s a lot of energy pent up in a five year old and that needs to go somewhere.
The other approach I would recommend (and they are not mutually exclusive) is to include him in whatever you are doing around the house. A five year old can participate (note that I avoid the term “help”, I am not talking about chores here) in doing laundry, cooking meals, cleaning up, small repairs, gardening,... - you will also teach him about “life” in so many valuable ways by just letting him tag along. Yes, after lockdown he probably won’t be able to do the family’s laundry, but perhaps start a pre-sorted load?