For Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/Tumbleweed/home:plater.repo
zypper refresh
zypper install meson
For Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/Factory/home:plater.repo
zypper refresh
zypper install meson
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/15.6/home:plater.repo
zypper refresh
zypper install meson