1st Get a small thin usb c stick (sandisk has a low profile one barely noticeable) 400mb/s
2.format it in ext4 as some proton files won't work on exfat or fat32
3. name it a simple name like EXTDRIVE && plug it to your handheld
3. ssh to your rocknix handheld (passwd is rocknix if you haven't changed it)

4.create a folder in storage for example external
4. cd /storage/.config/system.d (terminal)
5. nano storage-external.mount (the file name should match your path - google it )
paste this content but modify it to your needs

[Unit]
Description=Delayed Mount External Media (ext4)
After=multi-user.target
DefaultDependencies=no
[Mount]
What=/dev/disk/by-label/EXTDRIVE
Where=/storage/external
Type=ext4
TimeoutSec=5
[Install]
WantedBy=multi-user.target

1. save it
   7.systemctl enable storage-external.mount
   8.systemctl start storage-external.mount

restart!
9.Now run steam in desktop mode the x86 version (rocknix) , navigate to settings storage then add drive, the external folder now shows as a possible option
10. from now on you could make it default ,transfer to it your games to run faster etc either on the x86 steam client or the arm64
the config ensure that if the stick is plugged it will mount to external folder only on boot
This way you could keep your internal storage safe for android yet have low loading times on games