Reukra said that their no pokemon that perfect but a team that counter every weakness , every strategy.

is its possible to make a team like that?

No, and if there was then online battling in the main Pokemon games wouldn’t exist. The closest I can think of is Funbro (you trap a Pokemon which can’t 2HKO you and then stall them out until Struggle, then force them to stay alive with Recycle Leppa Berry and Heal Pulse. However, it doesn’t actually win as the opponent can just keep playing forever and it can be countered with a team that has a ton of Choice items/Taunt/Voltturn to prevent the strategy). Additionally, that team would not always win against itself. You can get pretty close with broken strategies like Baton Pass.

but is it possible to make a team that cover each other weakness but still have a great strategy?

That’s the point of every team.

Here’s how competitive Pokemon works: every good team is able to, at least to some extent, handle every Pokemon and team archetype. You’ll naturally be more weak to some things than other things but that’s unavoidable due to how many different Pokemon there are. There is such a thing as a team being “better” than another, but there is no such thing as a “perfect” team.

When I say “more weak” to something than something else, I don’t mean that you auto lose to it. For example, you could make a good team that’s solid all around and has answers to all the relevant Pokemon and archetypes. Let’s say that theoretically, your team is a little weak to Heatran. That doesn’t mean you auto-lose to Heatran (otherwise it wouldn’t be a good team), but that means that Heatran naturally pressures your team a little more than other Pokemon would.

However, if you try to modify your team to be a little better vs Heatran, then you are inevitably going to make your team a little worse vs something else. For example, let’s say you have a Latios that has Calm Mind, Draco Meteor, Psyshock, and Hidden Power Fire. If you change Hidden Power Fire to Surf to not be walled by Heatran, then you are going to be worse off versus Ferrothorn. If you trade Calm Mind for Surf, you are going to be worse off vs Clefable because you have no way to boost and break through it.

So there’s no such thing as a “perfect” team, but any good team, despite being slightly weaker to something than other things, has ways to deal with pretty much everything at some level.