USB3 data transmissions can radiate enough RF interference at 2.4 GHz to slow or even jam a WiFi connection.
I use 5GHz WiFi, but I have tested 2.4GHz and it worked okay when I tried it.
On the other hand, my 2.4GHz Logitech Unifying wireless keyboard/mouse dongle was having issues when directly connected to the Pi4's USB 2.0 port. Placing the dongle on a shielded USB 2.0 extension cable fixed it.
I did try adding some ferrite beads to my USB 3.0 SATA adapter cable, and that helped, but it didn't completely resolve the issue. So the dongle is back on the short extension cable (6 inch works for me, YMMV).
... every metal case on the market has a noticeable, negative effect on wifi
Compared to my 4B2 in a dual layer open sided acrylic case, my 4B4 in a Flirc case does seem to have a bit weaker reception, but it hasn't been a problem for me (yet). Unlike many other metal cases, the Flirc has a plastic bottom that extends a little up the end with the wireless antenna. So it should interfere less than full metal cases.
I have YouTube streaming video to my Flirc cased 4B4 on 5GHz WiFi right now (Auto 1080p), with audio going to my Bluetooth speakers, and the system was booted from a 64GB Samsung USB 3.0 flash drive. So yea, the Flirc case has some affect, but it hasn't been a deal breaker.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?