What if I install org-roam manually, should I require all those .el files ?
like this
(require 'org-roam)
(require 'org-roam-db)
(require 'org-roam-capture)
(require 'org-roam-compat)
...
;; extensions
(require 'org-roam-dailies)
(require 'org-roam-export)
(require 'org-roam-graph)
(require 'org-roam-overlay)
Because there’s no variable org-roam--sqlite-available-p in my Emacs
Interesting question. To be honest I manually install all my packages because I whole heartedly do not like wholesale upgrade … I don’t like to upgrade ever. But I skipped over installing org-roam the manual way because it has too many dependencies.
Are all the dependencies satisfied? I think that video is extremely dated probably. There doesn’t exist a variable as such that is known to me, or I can find using grep.
I think you are right, the video is dated.
Don’t remove files.
Leave in them in their own directory and modify the load-path and add their directory.
This way if there are any updates, you can simply replace the entire directory.
I’m not removing any file.
As a side note - I created a function that will download packages from melpa and then recursively download their dependencies, I found that org-roam doesn’t have many external dependencies - or dependencies of dependencies.
So for anyone trying to install manually,
dash emacsql magit-section llama
these are the only dependencies necessary.
Here is my function (Hidden as spoiler)
remember to refresh contents 
(require 'package)
(require 'url)
(require 'tar-mode)
(require 'bytecomp)
(defun packages-download (pkg-name dest-dir &optional byte-compile-p force-deps)
"Download PKG-NAME from MELPA, extract it into DEST-DIR, and optionally BYTE-COMPILE it.
Recursively downloads and extracts dependencies too.
When optional FORCE-DEPS is non-nil do not check if dep is already available."
(interactive
(list (intern (completing-read "Package: " (mapcar #'car package-archive-contents)))
(read-directory-name "Destination directory: ")
(y-or-n-p "Byte-compile extracted .el files? ")))
;; Refresh if necessary
(unless package-archive-contents
(package-refresh-contents))
(let* ((pkg-sym (if (symbolp pkg-name) pkg-name (intern pkg-name)))
(pkg-desc (cadr (assoc pkg-sym package-archive-contents))))
(unless pkg-desc
(error "Package %s not found in archive contents" pkg-sym))
(let* ((version-str (package-version-join (package-desc-version pkg-desc)))
(tar-name (format "%s-%s.tar" pkg-sym version-str))
(tar-url (format "https://melpa.org/packages/%s" tar-name))
(download-path (expand-file-name tar-name dest-dir))
(extract-path (expand-file-name (symbol-name pkg-sym) dest-dir)))
(message "Downloading %s ..." tar-url)
(url-copy-file tar-url download-path t)
(message "Downloaded to %s" download-path)
;; Extract
(make-directory extract-path t)
(let ((default-directory extract-path))
(with-temp-buffer
(insert-file-contents-literally download-path)
(tar-mode)
(tar-untar-buffer))
(message "Extracted %s to %s" tar-name extract-path)
;; Move nested contents up one level
(let* ((entries (directory-files default-directory t "^[^.]"))
(subdir (car (seq-filter #'file-directory-p entries))))
(when (and subdir (not (equal subdir default-directory)))
(dolist (item (directory-files subdir t "^[^.]+"))
(let ((target (expand-file-name (file-name-nondirectory item) default-directory)))
(if (file-directory-p item)
(copy-directory item target t t t)
(copy-file item target t))))
(delete-directory subdir t)))
;; Byte-compile if requested
(when byte-compile-p
(add-to-list 'load-path default-directory)
(byte-recompile-directory default-directory 0)))
;; Recursively handle dependencies
(dolist (dep (package-desc-reqs pkg-desc))
(let ((dep-name (car dep)))
(unless
(cond
((package-built-in-p dep-name) t)
((string= dep-name "compat") t)
((not force-deps)
(or (featurep dep-name)
(locate-library (symbol-name dep-name))))
(t nil))
(message "Installing dependency: %s" dep-name)
(packages-download dep-name dest-dir byte-compile-p force-deps)))))))