I have 2 machines running Solus, 1 updated with no problem, the other had this exact problem.
Upgraded lsof
[✓] Syncing filesystems success
[✓] Updating dynamic library cache success
[✗] Updating clr-boot-manager failed
[FATAL] cbm (../src/bootman/kernel.c:L668): Failed to install initrd /boot/initrd-com.solus-project.current.5.10.9-169: No space left on device
[FATAL] cbm (../src/bootman/update.c:L250): Failed to install default-current kernel: ///usr/lib/kernel/com.solus-project.current.5.10.9-169
[✓] Running depmod on kernel 5.10.9-169.current success
[✓] Running depmod on kernel 4.14.216-165.lts success
[✓] Updating mimetype database success
[✓] Updating icon theme cache: korla-pgrey success
[✓] Updating icon theme cache: Papirus-Dark success
[✓] Updating icon theme cache: korla success
[✓] Updating icon theme cache: Papirus-Light success
[✓] Updating icon theme cache: korla-light-panel success
[✓] Updating icon theme cache: Papirus success
[✓] Updating icon theme cache: korla-light success
[✓] Updating desktop database success
[✓] Updating manpages database success
I'm wondering what DE are you using and also are you using LVM?