Application design software?

Question

Project management

Hello everyone, this is the story. All my life I have been developing on my knee, but now I understand that it is difficult to develop more or less large applications with this approach. Previously, in order to remember what functionality, interactions and data types (entities) are used, I wrote everything down in Google Docs / Sheets, but this is not convenient, since there are no connections, etc.
Maybe someone knows some kind of design software?
UPD. I am making a client-server application, the client has a certain UI

Answer 1

UML and a more or less satisfying editor from the .

Answer 2

Enterprise Architect

Answer 3

Zeplin

Answer 4

Zeplin is the most convenient option