A systemd unit to bind /usr/local from offload is available, but masked by default

[jcotton42]

$ systemctl cat usr-local.mount 
# /usr/lib/systemd/system/usr-local.mount
#  SPDX-License-Identifier: LGPL-2.1+
#
#  This file is part of steamos-customizations.
#
#  steamos-customizations is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public License as
#  published by the Free Software Foundation; either version 2.1 of the License,
#  or (at your option) any later version.

[Unit]
Description=SteamOS Offload - /usr/local

[Mount]
What=/home/.steamos/offload/usr/local
Where=/usr/local
Type=none
Options=bind

[Install]
WantedBy=steamos-offload.target

However, out of the box this was masked (basically a stronger disable). On my own Deck I decided to unmask and start it, and it seems to work fine. This makes /usr/local writable, and it's stored on the home partition. Unsure why Valve decided to mask it.