I think i worked it out. You were right but it required some airtable magic aswell to happen on what to conditionally filter. My workaround is as following :
In airtable i have (for this purpose) 2 tables : Users and Applications
- I added in a date created (with time) field in the Applications Table. This autopopulates when the record is made.
- I made sure to send in a “hidden” form field the recordId of the user to link with the application.
- I added in the Users table a Rollup field with MAX(values) of the “date created (with time)” . This shows the date/time for the last application that the user has done.
- In the Applications table a made a new lookup field that looks up the last application of the user (from the step above).
- I then added a formula field (named last created?) that simply stated : IF({created date}={lookup_last created},“Last”,“”)
Returning to softr I added in 2 conditional filters on the list details block:
Users is any of Users
AND
Last created? is Last
This did the trick 
if anybody has efficiencies to gain by using URL params or something i am all ears. Feels a bit cluncky. Maybe add it to the submit button for conditional forms @Andranik ?