>> there is not enough budget to actually rewrote whole system,
As pointed out elsewhere, this is definitely solving a real problem, the longevity of the app is the proof.
Instead of rewriting, can you replace it with newer idioms? A MVP/PoC for a newer way of solving a problem (AR may be here) that the software solves with some tangible gains, the latter is more important, can lead to approval of a mini budget for that MVP and who knows what that can lead to.
Well, maybe. Biggest problem is using database from 80s, which is used in a way that sometimes it acts like database, sometimes it is used by copying files (one file per table) around random directories with custom locking mechanism.
App consist of maybe 20 different codebases that generate around 30 executables, kind of randomly, fetching source files from different codebases as programmer find a fit + random "fixes" of system modules/component make it all very very hard to do much groundbreaking work.
As pointed out elsewhere, this is definitely solving a real problem, the longevity of the app is the proof.
Instead of rewriting, can you replace it with newer idioms? A MVP/PoC for a newer way of solving a problem (AR may be here) that the software solves with some tangible gains, the latter is more important, can lead to approval of a mini budget for that MVP and who knows what that can lead to.