Happy to try anything that might help but I get the following when I try to install:
Fetched 483 kB in 4s (111 kB/s)
Reading package lists... Done
E: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/focal-security/main/binary-i386/Packages 404 Not Found [IP: 2001:67c:1360:8001::22 80]
E: Failed to fetch http://gb.archive.ubuntu.com/ubuntu/dists/focal/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.152 80]
E: Failed to fetch http://gb.archive.ubuntu.com/ubuntu/dists/focal-updates/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.152 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.
Edit: Tried to install it using sudo apt install, which worked. However it doesn't seem to open when I click on it in Ubuntu Mate now.