Removing Partitions

In theory you should be able to select each partition and click the "-" button to delete the partitions one at a time. Rinse & repeat. Then you can try to merge the empty area back into the main macOS partition/Container. Sometimes this does not always work so you may need to perform a clean install of macOS by first erasing the whole physical drive before reinstalling macOS and restoring from a backup. It is best to do this while booted into Recovery Mode or from a macOS USB installer. Note: Erasing a drive will destroy all data on the drive.

Deleting the partitions will not remove the Linux bootloader from the drive since the Linux bootloader is stored in a folder on the hidden EFI/ESP partition. You will need to delete the Linux folder on that hidden partition so that the Linux boot option no longer appears on the Apple boot picker menu. You may need to reselect the default macOS Startup Disk System Preference as well.

FYI, I never recommend anyone to create multiple partitions on the main boot drive because people usually end up in a situation like this which can potentially prevent macOS from booting and perhaps even losing access to important data. If users want to run another OS, then installing the other operating system(s) into a Virtual Machine is the safest option that is least disruptive to the main OS. If the other operating system(s) need to be installed on bare metal, then I recommend installing them to an external USB3 drive instead in order to minimize the risk to the main boot volume and data.

Before attempting to delete and merge any partitions make sure to have a good backup of any data on this Mac. Modifying partitions is a major task that is very risky and could lead to data loss.

You should always have frequent and regular backups of the computer (and each OS) and all external media which contains important & unique data.