In the restore options: set Don’t Save Owner to YES
Try the installers here: https://www.enterprisedb.com/downloads/postgres-postgresql-downloads .
In 9.6 (9.6.12 in my case) I haven’t seen a DB backup size limit so far, I’ve restored backups larger than 1 GB without any problems.
Hope this helps
I am currently using pgAdmin 4v3 with PostgreSQL 9.6 which works fine :)
You can find this version for download here
EDIT: took too long typing: what Dragos said