do-release-upgrade silently fails upgrading from 18.04 LTS to 20.04 LTS in WSL [duplicate]

I had the same issue. I thought I didn't have snap installed and there are no PPAs as far as I know. Checked out /var/log/dist-upgrade/main.log and there were no errors. Here's the output:

2021-08-05 16:57:53,055 INFO Using config files '['./DistUpgrade.cfg.bionic', '/etc/update-manager/release-upgrades.d/ubuntu-advantage-upgrades.cfg']'
2021-08-05 16:57:53,055 INFO uname information: 'Linux DESKTOP-514S07G 4.4.0-19041-Microsoft #488-Microsoft Mon Sep 01 13:43:00 PST 2020 x86_64'
2021-08-05 16:57:53,586 INFO apt version: '1.6.14'
2021-08-05 16:57:53,587 INFO python version: '3.6.9 (default, Jan 26 2021, 15:33:00)
[GCC 8.4.0]'
2021-08-05 16:57:53,601 INFO release-upgrader version '20.04.34' started
2021-08-05 16:57:53,648 INFO locale: 'en_US' 'UTF-8'
2021-08-05 16:57:53,820 WARNING estimate_kernel_initrd_size_in_boot() returned '0' for kernel?
2021-08-05 16:57:53,820 WARNING estimate_kernel_initrd_size_in_boot() returned '0' for initrd?
2021-08-05 16:57:53,870 DEBUG Using 'DistUpgradeViewText' view
2021-08-05 16:57:53,991 DEBUG enable dpkg --force-overwrite
2021-08-05 16:57:54,198 DEBUG creating statefile: '/var/log/dist-upgrade/apt-clone_system_state.tar.gz'
2021-08-05 16:57:56,401 DEBUG lsb-release: 'bionic'
2021-08-05 16:57:56,402 DEBUG _pythonSymlinkCheck run
2021-08-05 16:57:56,403 DEBUG openCache()
2021-08-05 16:57:56,403 DEBUG quirks: running PreCacheOpen
2021-08-05 16:57:56,403 DEBUG running Quirks.PreCacheOpen
2021-08-05 16:57:57,597 DEBUG /openCache(), new cache size 72355
2021-08-05 16:57:57,598 DEBUG need_server_mode(): can not find a desktop meta package or key deps, running in server mode
2021-08-05 16:57:57,598 DEBUG checkViewDepends()
2021-08-05 16:57:57,603 DEBUG running doUpdate() (showErrors=False)
2021-08-05 16:58:03,578 DEBUG openCache()
2021-08-05 16:58:04,857 DEBUG /openCache(), new cache size 72355
2021-08-05 16:58:04,857 DEBUG doPostInitialUpdate
2021-08-05 16:58:04,857 DEBUG quirks: running focalPostInitialUpdate
2021-08-05 16:58:04,858 DEBUG running Quirks.focalPostInitialUpdate
2021-08-05 16:58:05,643 DEBUG abort called
2021-08-05 16:58:05,644 DEBUG openCache()
2021-08-05 16:58:06,869 DEBUG /openCache(), new cache size 72355

It turned out I had snapd installed and removing it solved the problem.