How to handle divide by zero in GENERATED columns in MySQL
There are three ways to handle DIVIDE BY ZERO error in your case :

1) USING IF() :

ALTER TABLE report_user 
modify avg_trans_out_amount bigint 
GENERATED ALWAYS AS (round(trans_out_amount/if(trans_out_count,0,1))) STORED;


2) USING NULLIF() :

ALTER TABLE report_user 
modify avg_trans_out_amount bigint 
GENERATED ALWAYS AS (round(trans_out_amount/nullif(trans_out_count,1))) STORED;


3) USING GREATEST() :

ALTER TABLE report_user 
MODIFY avg_trans_out_amount bigint 
GENERATED ALWAYS AS (round(trans_out_amount/greatest(trans_out_count,1))) STORED;