I want to create a server with original 1.19 Craftoria.
But not all players can play original modpack, because of a lack of RAM.
Which mods can I delete, or any other improvements I can do to create a lightweight version of minecraft client but with the ability to connect to the original server ?
( server part will not change )

You can see all client-side mods by setting Allow content management for this profile on curseforge and sorting the mods by client env.

Unfortunately removing client side mods would not change the ram usage noticeably and its also not recommended as you could involuntarily remove a performance mod which would make things worse.

Here are the steps:

And removing any content mods could break the modpack all together.

Remember, all you need is 6GB. Most computers, even older ones, should have at least 8. Drop video settings, low render distance, and dont expect high fps. Unless your friends are playing on a desktop older than a decade, or a laptop older than half a decade, it should be somewhat playable.