I only discovered this since getting the new iOS version of Slack since it is more intuitive to find your preferences but you can change the browser slack opens links in.
For most apps I enjoy having a simple streamlined in-app browser. As long as it has a simple way to open the link in Safari, then I’m all for it. However I’ve always thought it was an awkward choice to have the in-app browser in Slack. A common use case is that someone shares me a link, the in-app browser takes over, I would have to close the link to respond to it. Then I would often want to refer to the link’s contents and would have to click in and then click close to get back out to continue the chat. I found this particularly frustrating on iPadOS where multi-tasking is so much better than on the iOS. After changing the Web Browser setting I can keep Slack open and have Safari in Split View and reference the content while chatting about it. Problem solved.
You can find this setting on the current iPadOS app by clicking the 3 dots in the upper right of any chat conversation, Settings->Advanced->Web Browser.
With the desktop and iOS app recently refreshed we can only hope they are working on a new iPad app which includes video chat and screesharing.