Your instincts were correct if you felt like NFL officials were throwing more flags in 2021. Penalties ticked up to 13.88 per game during the regular season, which was a bit higher than the 2020 season (13.14) but still way below where they were in 2019 (16.17) and 2018 (15.87).
That's the longer-term context you should watch this year's postseason games. It would be a surprise if we saw many penalty-filled games, and with any luck, we'll spend the next four weeks talking about the performance of players and coaches, and not about the fouls that were called (or uncalled) against them.