Are you using an Intel wireless chipset or the terrible Broadcom one that Dell used to use? Not sure what Dell was using in 2018, but I replaced the garbage Broadcom chip in my 2015-era XPS 13 with a much more reliable Intel model, and most of by bluetooth problems were immediately fixed.
That said, the replacement process is pretty fiddly...Dell likes using lots of very small screws made of very soft metal.
I've also found that Gnome's bluetooth handling varies from barely acceptable to confusingly horrible. KDE's bluetooth handling has been way more reliable for me across multiple machines and distros. So the problem may very well be in userspace.
I have the XPS13 9380 (also 2018), and it came with an Atheros WiFi chipset (Killer, I believe). Looks like the Bluetooth is on separate hardware here; lsusb reports it as a "Foxconn / Hon Hai" chipset.
I don't really use BT for anything, so I can't comment on its quality. WiFi has been completely fine, though. Either way, I believe both the WiFi and BT hardware are soldered in on this model.
That said, the replacement process is pretty fiddly...Dell likes using lots of very small screws made of very soft metal.
I've also found that Gnome's bluetooth handling varies from barely acceptable to confusingly horrible. KDE's bluetooth handling has been way more reliable for me across multiple machines and distros. So the problem may very well be in userspace.