FIFA has about 6 international windows each representing about 9 days each. These windows are used for for friendlies, qualification games, and a mix of other games, particularly in Europe with the Nations League.
There are also quadrennial release windows for the continental cups and world cups which last the entire length of the tournament so long as your team is still participating.
For ordinary release windows players are released for 4-5 days per scheduled official match (depending on whether the player flies cross continental), and only 2 days if it's a friendly.
Clubs will (at least publicly) rarely kick up a fuss when it comes to true international fixtures, but lots of players will have niggles coming into a window where their team is only playing friendlies.
Football "works" (people can argue not well enough but I digress), because the Clubs are the primary product, with the World and Continental association holding just enough power over things like the Champions League to ensure a reasonable International game continues to be in place.