How can I remove a recovery partition and merge two data partitions on an external SSD?

Those EFI and recovery partitions were likely left over from the SSD’s previous role as a Windows boot drive. They aren’t required just because the data partitions use NTFS, and NTFS partitions do not need matching recovery partitions. If you want to keep the existing data partitions, you could delete the 450 MB partition with a suitable partition-management tool and then extend the first NTFS partition into the now-unallocated space, but the unallocated space must be directly beside the partition you want to enlarge. Since nothing needs to be saved, deleting all partitions and starting over avoids the layout and resizing complications.

Since the drive contains no data you need, the simplest and cleanest solution is to delete every partition on it and create one new partition using the full capacity. Disk Management usually won’t let you remove every protected EFI or recovery partition through the normal interface, so use an elevated command prompt with DiskPart: run DiskPart, list the disks, select the correct external drive by its number, use `clean` to remove its partition table, then create and format a new partition. Double-check the disk number first, because `clean` permanently removes the selected disk’s partition information.