I see that many more organizations use Discord instead of Slack nowadays. For example, the last 2 that I joined use Discord and not Slack and there is no problems with spammers mostly:
Looks like Discord won.
I'm a moderator on a Discord server with a ~1000 users myself and we only get a spammer once in half a year, and messages are very easy to delete and ban them with a single command using a chat bot.
Could be worth a try to use Discord.