Apologies for the very delayed response. Sample scripted functions are provided on a best effort basis and with the backlog of support from the holidays, we haven't had a chance to work on these yet. I hear you on the post not being acknowledged and we'll make sure to do that in the future.

For your first request this can be acomplished with two scripted functions and Window Created/Process Created and Process Ended triggers. The first scripted function presses the ALT button, the other releases it. The triggers will control when these functions get used. Below is a screenshot of these triggers set up for Battlefield 6:

NotFound:press alt trigger.png
NotFound:release alt trigger.png

For your second request this can also be done with a scripted function to end the Steam process and a Process Ended Trigger. You'll need to set up a new Process/Window created trigger for each of the games you would like steam to exit with. Below is a screenshot of a trigger I've set up for Factorio:

NotFound:close steam trigger.png

I've attached all of the scripts necessary to this post. You can import them via the DisplayFusion Settings > Functions > Scripted Function > Import Scripted Function.

To set up the triggers, you can create a new Trigger by pressing the DisplayFusion Settings > Triggers > Add button, and copying the examples from this post.