I’m not a frequent user of Google Sheets, so whether my answer is of value is up to you.
But AFAIK the document link (X-devonthink-item://...) can be used in any document on macOS, iOS or iPadOS as long as that program considers it a hyperlink. E.g. pasting the link in Notes on iPadOS and clicking it opens the corresponding document in DTTG.
Perhaps Google Sheets doesn’t consider it a link if the first characters of the URL don’t start with http, https, ftp etc.? It appears so, as pasting it into a cell results in an error where Sheets asks whether a typo was made.
I tried it in another Web app where I created a blank document and Safari won’t resolve the link, although you can paste the link in the Safari address bar and open the URL locally (at least on an iPad and DTTG).