If you want to be online, but want to block internet to certain apps like work apps, messaging apps etc, and continue using rest of your apps, you can do it using this app.
And no,this is not an ad. https://play.google.com/store/apps/details?id=dev.tuantv.android.netblocker
Afwall+ if you’re rooted is by far the best app for this.
Next up of you’re not rooted is RethinkDNS.
Both superior to this app imo.