Want an automated "static" date/time which doesn't update when sheet is recalculated

I'm trying to create a mobile friendly sheet where I can quickly input the current date/time and not have it update when the sheet is recalculated. The screenshot has the date/time populate if I select a check-mark. However that doesn't survive a recalculation and I can't figure out a way to do it. I know about the simple use of CTRL; and Shift CTRL; on desktop, but those aren't great for mobile entry with Gboard.

Any suggestions?

Screenshot