Link Aggregation… No. MULTIWAN yes.
It does either fallback, where if one wan dies it swaps to another, or Load balance where you can tell it to use one wan or the other based on how many connections are going out.
Link aggregation (LAG) is pulling data from 2 connections at the same time OVER ETHERNET. So that means you need a main modem/router from your provider that supports it AND your router (in your case the flint ax1800) must be compatible. As far as I know LAG is NOT available on the AX1800 but that said I haven’t tried because I don’t have a LAG capable main.