The following is an assumption:
Since you say you are new to this, I figure someone set it up for you and since then you never shut it down.
Now, after RetroArch crashed your Switch, which probably occured when trying to launch it through Album to access hbmenu, not holding R while launching a game for title-override which is recommended for homebrew apps like RA, you attempted to "just boot" it without injecting a payload, resulting in booting to stock HOS (HorizonOS, Switch firmware).
The person who set it up probably also did setup an emuNAND for you, which is good to begin with, because it would explain your games suddenly missing.
First, read this for some general knowledge
https://rentry.org/SwitchPayloadLaunch and then
read step 1 and 4 of this guide
https://rentry.org/EristaEmuNAND to launch back to your emuNAND, mind that you probably can skip the part of step 4 where it tells you to create an emuNAND, first check if you already have one which is explained later.
Precisely, you need this (download links are at the top):
View attachment 321693
View attachment 321691
View attachment 321692
If something doesn't work, check the rest of the guide from top to bottom and follow it's instructions for setting up, before you then try it once more. If no emuNAND exists (which would be indicated by an E (E = emuNAND, S = sysNAND, nothing = stock) at the end of the update string in system settings), create one.