Chrome-based browsers not downloading files

Hi again
Sorry to bump this - however, the issue appears to be getting worse.

I used to be able to download files using any browser. However, this is no longer the case. Chrome and now Brave do not download any files, even though the file/ destination selection window appears, nothing is transferred.

I have transferred work-related materials to Vivaldi for expediency, but this really isn’t okay because one of the fundamental functions of a web browser is to be able to download web-based materials. Hence, this feels like a broken functionality that I’d like to try to fix if possible.

I’d really appreciate any advice - I have reset all the browsers in question to their default settings, I’m not sandboxing anything, and since Firefox still works as expected, it isn’t my ISP/ Net connection either.

I’ve added the output from printenv if this means anything to someone with a better grasp of these things than me:

SHELL=/bin/bash
SESSION_MANAGER=local/valhalla:@/tmp/.ICE-unix/920,unix/valhalla:/tmp/.ICE-unix/920
WINDOWID=67110388
COLORTERM=truecolor
XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0
LC_ADDRESS=en_GB.UTF-8
LC_NAME=en_GB.UTF-8
DESKTOP_SESSION=mate
LC_MONETARY=en_GB.UTF-8
EDITOR=nano
GTK_MODULES=canberra-gtk-module
XDG_SEAT=seat0
MATE_DESKTOP_SESSION_ID=this-is-deprecated
PWD=/home/andy
LOGNAME=andy
XDG_SESSION_DESKTOP=mate
XDG_SESSION_TYPE=x11
XAUTHORITY=/home/andy/.Xauthority
XDG_GREETER_DATA_DIR=/var/lib/lightdm-data/andy
MOTD_SHOWN=pam
HOME=/home/andy
LC_PAPER=en_GB.UTF-8
LANG=en_GB.UTF-8
XDG_CURRENT_DESKTOP=MATE
VTE_VERSION=8001
XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0
XDG_SESSION_CLASS=user
LC_IDENTIFICATION=en_GB.UTF-8
TERM=xterm-256color
GTK_OVERLAY_SCROLLING=0
USER=andy
DISPLAY=:0.0
SHLVL=1
LC_TELEPHONE=en_GB.UTF-8
LC_MEASUREMENT=en_GB.UTF-8
XDG_VTNR=7
XDG_SESSION_ID=2
XDG_RUNTIME_DIR=/run/user/1000
DEBUGINFOD_URLS=https://debuginfod.archlinux.org 
LC_TIME=en_GB.UTF-8
GTK3_MODULES=xapp-gtk3-module
XDG_DATA_DIRS=/home/andy/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share
BROWSER=firefox
PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/var/lib/flatpak/exports/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/home/andy/COMPUTER-
GDMSESSION=mate
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
MAIL=/var/spool/mail/andy
QT_FONT_DPI=96
QT_SCALE_FACTOR=1
LC_NUMERIC=en_GB.UTF-8
_=/usr/bin/printenv```

<Edit: Thanks Cactux - I used the BlockQuote option but have now amended as per your suggestion>
I tried switching themes but that doesn't appear to have had any effect, and I have no idea if this is Mate-specific. 
I have now added a new user with the KDE and everything works as expected in both Brave and Chrome.
This means that it is a DE issue, so I will now raise this in the Mate section of the Forum.

Cheers