SharePoint Migration from SP2013 to SP2019

Hi All,

We are planning to migrate from SP2013 to SP2019. Could some one help me the possible challenges or issues can we address or face while doing this migration. 

I am looking mostly in prospective of below :- 

1. Possible End Users issues/ impact

2. If we change to Modern List and Library what possible issue/ impact

please help me.   

Thanks,

Manoj