I know that OpenSUSE uses a new file system so cannot go onto its drive in Ubuntu so how do I clear out the /tmp folder to allow it to boot?
How were you trying to “launch”? What exactly do you mean by launch error? What exactly does “errors out” mean? What kind of computer is this? What model? How old is it?
The relatively new default BTRFS filesystem is not mandatory. You can still choose to use EXT2, EXT3, EXT4 and others.
so cannot go onto its drive in Ubuntu
What does “its drive in Ubuntu” mean? Are you trying to add Tumbleweed to a disk that now has a working Ubuntu on it? Are you wanting to replace Ubuntu? Is there anything else on its HD?
so how do I clear out the /tmp folder to allow it to boot?
Allow what to boot? The openSUSE installation medium has no valid reason to care about any /tmp folder that’s on a disk with Ubuntu on it. The TW installer may be announcing that one or more filesystems has/have little or no freespace, but it’s normally just a warning, not a reason to stop proceeding with a new installation of a different operating system than is currently present.