Single vertical row of keys not working anymore

Hello,

a vertical row of keys on my 2020 Macbook Air M1 first stopped working intermittently and now ceased working alltogether (9,o,l,. keys). There was no spillage/physical damage that I am aware of. Unfortunately, the MacBook is out of warranty by now so the Apple Store won't replace anything. I don't trust myself replacing the keyboard on my own and a whole upper case is 300$... Is there anything else I might look into checking (flex cables, connectors, etc.) that might be at the origin of the fault and is cheaper/easier to replace than the whole keyboard?

Many thanks!