The understanding of vue-router

I thought vue-router was very simple and easy to understand, and I really used it. I found two problems:
1, the vue-router routing page cannot be added with .html, otherwise there will be no routing page
2, after the code build is deployed on the server, the page cannot be refreshed, and the page will be refreshed directly on 404. This official website seems to need backend configuration.
how to understand these two questions well?. Furthermore, can it be solved through some front-end settings of vue-router?

Mar.11,2021

https://a.com/user/account
a.com corresponds to a folder on the server, and user/account is a resource under the folder. Because vue-route, is used, these resources do not exist in this folder, so 404 is returned. So the server needs to do url rewrite, to point all requests to index.html. This file is real.

most of the servers are officially configured: https://router.vuejs.org/zh-c.

or use the default hash method,
https://a.com/-sharp/user/account, where the content after the # division symbol is the path of the server, just some parameters (even understood as comments), (and URL for the first time? Is the GET parameter delimiter and will not look for it, so there is no need for the server to do any processing, because all requests are directed to index.html.

should be able to solve the second problem.
the first question is not quite understood. Adding .html is another resource.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1ea67c5-47b9d.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1ea67c5-47b9d.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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