Hello @Michele, welcome to the very struggle many of us are witnessing. Here is an ideas post that speaks to this issue. Fix custom field usage for Assets in FreshService - display_id is not available - Ideas - Freshworks Developer Community
There are a few other posts on this forum where this issue is brought up with no solution currently.
My suggestions in other posts have been to create middleware to work around these limitations. Dump your asset data into a database you manage and have your applications interact with that database. A lot of overhead, I completely understand.
Sorry I can’t be of more help here. But I feel your pain!