Currently, there are no particular restrictions on simultaneous access to the website.
However, if the CPU or memory resources are insufficient, the display speed may decrease.
As a reference, please also refer to the following articles.
On the other hand, there is an upper limit for the number of connections to the database.
Therefore, resource shortages may occur when processing that involves accessing the database using a plug-in, etc.
For sites that are likely to be accessed intensively, please consider using a CDN or cache plug-in.
For information on reducing the load on the site, please refer to the following article.