Back test period for EA



I made a EA and define all my indicator and  variable base on 1 year back test ( i made a optilimazion  and chose to best result )

1. when i run it for  2019-2020 ( 1 Year ) my EA was work perfect 150 trades with 20% Relative drawdown and very good profit 

but when i try to run my EA for 2 years back test to picure was differnet 

2. when i run it for 2018-2020 ( 2 year )  my EA the made 300 trades but  Relative drawdown went up to 80% and the profit was went down by far

( for 2018-2019 the EA loss 80% and from 2019-2020 the EA recover and finish with profit )

i know that the market change but how can i know what is the reliable period to test my EA ? 

if i have very good result for 1 year its   enough ?  despite when i run it on 2 years its not work good ? 

or 2 years its the best period to run back test ?