High memory usage - sql crashes

I use the 4.30 version. My server has 18 gb of Ram and 20 Processors. There are 35 Websites. But the sites make high memory usage. Mssql is swelling. The sites are not opening, they are closing.
Need help with the subject ?

Note:
1-The images are backed up in the folder (File System is Used). It's not in the database.
2- Log is not active.
3-recaptcha is defined all over the place.

RE: "Mssql is swelling"
Profile the queries.  Add indexes.

RE: "The sites are not opening, they are closing"
Check the System > Log for more specific error messages

There is no error message that the site is down.  How to add a directory.  Can you open?

RE:  "...How to add a directory.  Can you open?"
?
Please clarify?


(Note, that in general for ASP / SQL,  it is recommended to have separate servers. One for IIS, and the other for SQL Server.)

Re: Profile the queries.  Add indexes.  
  
I don't understand this?


RE: Note, that in general for ASP / SQL,  it is recommended to have separate servers. One for IIS, and the other for SQL Server.

what do you mean. It is necessary to use two different servers.  So SQL and IIS shouldn't be on the same server?

Re: Profile the queries.  Add indexes.  
Although the 'profiler' is technically deprecated (the new 'tool' is 'extended events'), the idea is the same...
Do some performance analysis on your SQL Server to identify which queries are taking a long time to run.  Then, you can run those queries in SSMS and get 'suggestions' as to what indexes you should create.


RE: Note, that in general for ASP / SQL,  it is recommended to have separate servers. One for IIS, and the other for SQL Server.

Yes, it is recommended to use two different servers.  SQL and IIS shouldn't be on the same server.
(But you may want to do some 'performance testing' to prove it in your case.  Also, note that have separate servers is more secure, because you don't need to provide public access to the DB.)

Thank you for your advice. But the problem is not solved. Does anyone have a different suggestion?

More memory.   (64 GB or more)
And, see configuration options
https://learn.microsoft.com/en-us/sql/database-engine/configure-windows/server-memory-server-configuration-options?view=sql-server-ver16

Similarly, IIS Manager "Advanced Settings", to set Private Memory Limit and Virtual Memory Limit in the recycling section.

Wouldn't 400GB be too expensive?  My server also hosts 15-20 sites.

Thank you for your help.  A definitive solution is needed.