How to respond/be supportive when a fearful avoidant partner withdraws? 28F 26M

My (28F) partner (26M) and I have been together for 9 months and I believe he might be a fearful avoidant.

In the past when we have had bigger disagreements, he completely withdraws and stops replying to messages. It’s like a switch flicks in his brain and he goes from being someone who is normally very understanding and reflective, to someone who can’t be reasoned with.

I try to be very selective with my words so they don’t come across as aggressive but he will become fixated on one thing that I said which he perceived as an attack, then self deprecate or sensationalise in response e.g. “I guess I’m just a horrible person” and then disappear for hours or a day or two.

He will occasionally send me bids for attention on other apps, like a funny reel to watch or send emojis/offer help in an online game we both play, while still actively ignoring the text conversation where we had argued. This drives me crazy cause it feels like he’s testing the waters to see if I will respond fondly to him, without addressing the issue at hand.

I used to chase him when he disappeared as the silence would fill me with anxiety but I realised this only made him feel more overwhelmed. However I am still the one who ends up reaching out and bridging the gap.

The only time this hasn’t been the case was during our last argument when he disappeared without a word for more than a day and I rage quit the game we play together in response because I was totally overwhelmed. Only then did he start chasing me and saying that he couldn’t handle the silence and he missed me… maybe because he lost the ability to gauge my interactions with him on that platform.

So I’m wondering what the best way is to respond when a FA goes silent? I don’t want to play games for his attention but me withdrawing last time prompted him to reach out first. I’m also scared to think how long he would allow the silence to continue if I don’t act or reach out first.

And how do I then circle back to the original argument to gain some kind of resolution, without him feeling attacked or dragging it out?

TLDR; partner disappears after big arguments. What is the best way to respond?