I can't merge two partitions on my MacBook Air

Sounds like the merge is going the wrong way. You appear to be deleting & merging an Apple Container into a small EFI partition (FAT). I don't think this is what you really want is it?

Merging partitions back together is not very easy or a straight forward process with macOS. Many times it is impossible to merge the partitions. Usually you are better off starting completely over from scratch by performing a clean install of macOS by completely erasing the entire physical SSD before reinstalling macOS & restoring from a backup. This is why I never recommend using multiple partitions on any drive. If you want to install & boot Linux on bare metal, then install Linux to an external USB3 SSD instead...very easy to get rid of Linux if you no longer want it. Or install the secondary OS into a Virtual Machine if the computer has enough resources to allow for the necessary workload in the guest OS.

FYI, in the future please rotate your pictures correctly before posting them online. It is very annoying having pictures side ways & upside down. Most times I will completely ignore a thread like this. You can easily rotate pictures on your iPhone/iPad by using the instructions in the following article.....I'm sure if you are using an Android device there is a similar way to rotate pictures:

https://www.iphonelife.com/blog/5/tip-day-how-rotate-photo

Back it all up, erase, re-partition, and reload.

Sometimes the whole point of storage partitioning is seemingly to lose any unbacked data, and to randomly require offloading everything and repartitioning and reloading whenever anything goes weird.

With any mixed operating systems, experiencing partitioning corruptions also unfortunately tends to a little too common for my preference. In years past, Windows was notorious for stomping on other systems’ storage with its fondness for writing a “harmless signature”, too. Mixtures don’t always play well together.

What to do generally? Running as a guest in a hypervisor is a bit more flexible and far more reliable as now you’re dealing with files and nit partitions, or booting and running each from a dedicated storage device. Separate boot devices will also be easier than stuffing several (functional) things into 256 GB.