I think that's wrong, national teams usually have a tactic, the coaches there do know which players they want to call up, at least few days prior but usually even longer, you have a whole pool of players that you could get. Which means coaches do know what they want to do.
Coaches of national teams know what their plans, tactic and training sessions are but with limited time of each international call up and training, it is not enough for coaches to help players have good bonds and sometimes they fail to practice the idea of coaches in match.
Problem is that players do not know that, if they haven't been the same roster of course, some nations have the exact same roster for few years, maybe one or two changes but that's fine, and in that case they can play perfectly well together, but some teams have a bit more new players, in that case it is coaches' job to explain to people what's going on, and what they are planning on doing and what the tactic will be.
The dependence on how on national squad is built. Some national teams have stable squads but some don't. With squads with many changes from reconstruction or as a consequence of a new coach, they will get troubles.
Players are playing for big clubs would be very tired with their responsibility in clubs and with a few days to rest between matches. Covid-19 breaks schedules of leagues, cups and players are in pressure of playing many matches in short time.
I still think that everything is ready when the game starts, I haven't seen any decent coach end up getting an upsetting result with great players, if you have the players, and a good coach, you win the game, doesn't matter how recently they got together.
With international team, problems are how to connect star players as a squad, not an issue of how many stars in one squad. Many big nations fail: Arghentina with Messi, Di Marid, Kun Aguero, Dybala, Higuain, Mascherano is good example. They are stars and play very well in clubs but under the Arghentina kit, they play worse than usual.
