after update (sudo apt full-upgrade) Cinnamon won't render

[Simon Garrett]

After an update today (can't remember what was updated), Cinnamon desktop renders only as grey and white rectangles, no text visible. I found a similar problem logged at https://github.com/linuxmint/cinnamon/issues/10254, which suggested "Report the issue to ubuntu against xorg or mesa."

Running:
Distributor ID: Ubuntu
Description: Ubuntu 20.04.2 LTS
Release: 20.04
Codename: focal

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.35
ProcVersionSignature: Ubuntu 5.4.0-80.90-generic 5.4.124
Uname: Linux 5.4.0-80-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Thu Aug 5 10:48:55 2021
InstallationDate: Installed on 2019-05-18 (809 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: dist-upgrade
UpgradeStatus: Upgraded to focal on 2020-05-13 (448 days ago)
VarLogDistupgradeTermlog: