The Speed is slow when map SharePoint 2019 as Network drive

I am helping client to map SharePoint 2019 as Network drive, which they complaints on followings:
1) the speed is very slow while copying and open file.

2) only allow less than 50MB file to be copy into network drive, which I had increase file limit in SharePoint Server and registry.
Folder copy error message when downloading a file that is larger than 50000000 bytes from a Web folder (microsoft.com)

3) Would like to ask how to count the Japanese & Vietnamese filename limit. For Vietnamese filename, it can display correct error when exceed 400 characters, but if Japanese it just show "Sorry, there was a problem uploading this file. Please try again".

Appreciate some expert can help on my issues.

Thanks.