The best thing I found is to set the broadband to broadcast at 5Ghz/2.4Ghz meaning 2.4GHz only devices are separated from the 5Ghz. With the independant channels it means that will cut back in interference or bandwidth hogging. Also boosters can amplyify things unncessarily, so Wireless N and faster speeds should be yield more bandwidth than the older G standard which peaked at 108Mbps which dual attennae and MIMO enabled.
Try resetting the router and reconnecting each device, by forgetting each one as suggested until you find which one is causing issues. Sometimes a router setting such as Wireless signal optimisation can reduce amount of bandwidth allocated to a device even after you disconnect it.
On a basic level then, set all 5GHz devices such as mobile devices to that frequency and legacy devices to the slower/less resource hungry 2.4GHz instead. You will find it works more efficently and any local devices which can work over ethernet so there is no conflicts.
I hope that helps.
Samsung Galaxy S10, Samsung Galaxy S21 Ultra
