Some of them do! Not my favorite team though… Atletico Mineiro had for a long time an official calendar, but it sucked! They had an event that showed up everyday called “Team’s Practice” – which I put up with for years! – but a couple of years back they just stopped updating the calendar, which led me into looking for alternatives. So this is more like an option in case the team you root for doesn’t have an official calendar you can subscribe to.
There’s also other alternatives like https://fixtur.es/en/, but they’re usually limited for teams outside the main competitions (e.g., Europe’s top divisions).
For example, the Brazilian team I support (Atletico Mineiro) plays its regional tournament (Campeonato Mineiro) from Jan until mid/late Feb, which doesn’t usually show up in these services. Since Atletico doesn’t have an official calendar, for 2-3 months I don’t really get the schedule using something like fixtur.es. For the 2023 season:
Footcal tries to fix this by using a source that has more tournaments than others sources. I basically developed it for it to work for Atletico’s calendar, but thought it could be helpful for others too :)