Anything can happen but I highly doubt that Leipzig will lose to Arminia, but like you have there is a possibility if we look at the past game for Leipzig VS Arminia, on December 18, 2021, Arminia won the game with 2 - 0 an upset for RB Leipzig playing at home, but if Leipzig could win this and Leverkusen lose to Freiburg if I am not wrong with how the Bundesliga give score to teams, Leipzig could end up on the 3rd place, and with their upcoming match against Freiburg, on DFB-Pokal if Leipzig wins then there can be a bright future coming for Leipzig in next season of Bundesliga,
Leipzig can't overtake Leverkusen anymore, they are 4 points behind with only 1 game left. It would have been of no significance anyway. Leipzig will need a draw to safely qualify for the Champions League (4th rank). Only Freiburg is threatening them who has to play against Leverkusen coincidentally.
I think Leipzig will get at least 1 point from their game, rendering the Leverkusen vs Freiburg game insignificant. I don't think Freiburg would win it though.
Leverkusen have secured a ticket to the Champions League next season. Now there is hope for Freiburg to replace Leipizg with a record that Leipizg must lose against Bielefeld. However, this seems impossible because Leipizg against the relegation team of course they have a big enough chance to secure 3 points. Leverkusen match against Freiburg will also be exciting although a win won't change anything for leverkusen but they will play at home for sure they will give their supporters a win for the last game of the season.