pi@lucas:~ $ sudo snap install slack --classic
error: snap “slack” is not available on stable for this architecture (armhf) but exists on other
architectures (amd64).
well, the snap is maintained by slack themselves, you would have to ask them to enable building for armhf …
but this means for them to enable testing, QA, bug tracking too for this architecture.
after all slack is a commercial product… the armhf userbase might not be a large enough target for them to justify investing that much money into it. so my suspicion would be that your chances are low to convince them to do this …