Slack suddenly stopped working on Ubuntu 20.04

Looks like there is a confirmed issue with the snap package.

We’re very sorry for the trouble there. We are experiencing some difficulties with the Slack Snap package. Our team is working hard to resolve the issue as quickly as possible. For now, you can access Slack via a browser or on our Direct Download version: https://slack.com/intl/en-gb/downloads/linux?eu_nc=1

Source: https://twitter.com/SlackHQ/status/1280808281989152771

A fix should be available in the next snap slack package release.

Slack 4.7.0 seems to be the issue. Contrary to one of the comments above, it is entirely possible to install an older version, which is one of the key features of Snaps...

To revert back to the previous version of Slack, use sudo snap revert slack:

$ snap list --all slack
Name   Version  Rev  Tracking       Publisher  Notes
slack  4.4.3    24   latest/stable  slack✓     disabled,classic
slack  4.7.0    25   latest/stable  slack✓     classic

$ sudo snap refresh slack
snap "slack" has no updates available

$ sudo snap revert slack
slack reverted to 4.4.3

Try to update again when there is a version above 4.7.0. This resolved my issue on Ubuntu 18.04 which exhibited the same issue (try to launch then immediately closes).

I fixed this problem by removing the snap and installing the deb instead. https://slack.com/downloads/linux