I have ADD. Diagnosed medicated 30 years ago as a child. Slack distraction isn't my specific achilles heel, but I think I get it.
What works for me is breaking up workdays into 3-4 parts. I physically move, rearrange my desk, restart my laptop, take breaks, close files and such to punctuate day parts and keep them distinct. I need a lot more than a timer to make this work.
Once I have the day split into distinct parts, I can deal with 2hr blocks at a time, rather than a whole workday. Whatever your specific difficulties are, I find they're more tractable within a 2hr block. Maybe you allocate 30m to slack and then close it.
I tend to "lay out my tools." Open only the files and apps that I need for the current block, print out my notes, stuff like that. Imagine laying out tools and parts before starting to assemble a piece of IKEA furniture. Then you put that stuff away, grab some other stuff, and start to work on fixing the sink.
The details are emergent. At least for me, this method is useful in the abstract. Whether the issue is slack, procrastination, big getting in the way of small or the reverse... I seem to find solutions much more readily within these smaller blocks of time.
I don't know if what works for me will work for you, but if it does... the way it works is that solutions to problems like your slack problem are easier to find when you just need to solve them for the next couple of hours.
I find I spend a lot of mental effort trying for big solutions to big problems, and besides medication, very few big solutions stick. Small solutions otoh.. seem to emerge once the framing is correct.
Also, not everyone is cut out for highly collaborative work. I'm not. I need decent size blocks of work that I can take and own. I'm just not reliable enough to have others depend on my work on a "by lunchtime" schedule. That doesn't mean I can't collaborate. I have managed teams and worked in people roles. I just can't work and have a conversation simultaneously. Instead, I will allocate a whole 2 hr block of time to pair programming-like modes.
If your solutions are good and you have confidence in them, workplaces tend to be flexible enough to contain them.