Everything you need to do is on this single page, no scrolling needed.
BTW, you might get away with just the last 3 of those commands. If you do not see a list of available packages after apt-cache showpkg openhab2 then run all 5 commands.
I have not used pishrink but . from looking at the documentation, you should be able to shrink it. If you want to be safe, copy the img and shrink the copy. If it does not work, you st.ll have the original img.
I assume you need to do this from a Linux system with an SD Card reader and use the dd command. The command, following the example in this thread, would be sudo dd if=~/raspbian_backup.img of=/dev/sdb
Sorry, had to step away for a bit. The first command sudo apt-cache show openhab2 should show all the listed options and you can pick from any of them. So if you see 2…4.0-1 listed as an option then yes the next command will downgrade you. If you do not see this then run all five commands one at a time.
Now that you’ve verified downgrading works you can upgrade to test when you have time. If Alexa still won’t find all devices then downgrade till another day.
I would also use openhab-cli to make a backup and install a fresh image on a different SD card and once OH is running on 2.5 then install just the binding needed for Alexa to work. If that works you can manually install your other binding or remove all bindings and try the openhab-cli backup restore.