Destiny 2 has always gotten a Power level increase with each new expansion, and the same happens for the game’s Seasons. When Destiny 2 first launched, the maximum Power level at the time was 300. It has grown with every expansion since, maxing out at 950 with Shadowkeep, although 960 was achievable from Pinnacle Gear.
Season of Dawn has bumped that up again, and the max level is now 960, and 970 with Pinnacle Gear. Where it gets a little confusing is the effect of seasonal artifacts such as Season of Dawn’s Lantern of Osiris. As you level up the Lantern, you also benefit from getting an increase in your Power level. This increase is temporary and only lasts for the duration of the season. When Season of Dawn ends, the increased Power is lost, and you will need to start building it up again next season.
The season artifacts allow players who may not be able to get their hands on Pinnacle Gear to stay increasing their Power level and even exceed the current cap. How beneficial this remains is up for debate, but it’s something to grind for as the season goes on, and should buy players a bit more comfort in endgame content than they might otherwise have.
All you need to do to keep increasing your Power level is to play the game. As you earn experience and level up, your season artifact will level up with you, giving you the extra Power levels you seek.