Having to focus on two competitions, especially now that these two competitions are quite important for Arsenal, will of course make them very tired and it cannot be denied that in terms of pressure, Bayern Munich is a little more advantageous now because they only focus on the Champions League match.
The fatigue factor will be quite influential on a team's performance, especially when one of them does not go according to expectations, which will certainly cause a team's mentality to decline further.
And for now, looking at the first leg between Arsenal and Bayern Munich, I don't think there are any obstacles for either team, I don't think there are any special reasons that are worth discussing from now on.
So far consistency and player injuries have often been problems that make Arsenal lose the chance to championship, the depth of the squad owned by Arsenal is currently not enough to convince to compete in two tight competitions at this time such as the EPL and UCL, when Arsenal lose several important players it is certain that their performance will decline dramatically like the previous season and this is what should be a job that should be Solved by Arteta before, but I think for now Arteta must be able to overcome the problem by rotating players like in their game yesterday.
Honestly for now I wouldn't underestimate Bayern Munich even though they are at their lowest point in the league, because so far Bayern Munich is still a big club that does have a better mentality and experience than Arsenal in the Champions League, and as you said, Arsenal are competing in two different competitions so it requires them to keep their focus and stamina as best they can at the moment, As for Bayern Munich, I think they no longer care about the Bundesliga at the moment so destroying Arsenal in two legs is the main target and focus of Bayern Munich in my opinion.
I don't yet consider Arsenal to be a team that has a winning mentality for any competition, but they are struggling to get that through their failures. Arsenal's squad is getting more mature and every player already has experience from previous failures, so this season they have to be better, especially when they still have a glimmer of hope of winning the title.
The quarter-finals were not easy for Arsenal, but considering Bayern Munich's inconsistent performance in many domestic leagues, Arsenal certainly has the opportunity to win a ticket to the semifinals. The match is expected to be tight with several goals scored by each team, but I don't imagine a draw.