When sending a JPG image fromLightroom Classic to Photoshop tif image not created

In this instance you do not truly have the stated filename open for editing. Only a - as yet unsaved - new image version held in memory alone, which has derived from a source file (plus the adjustments made in LrC). For lack of anything else to label it by in the meanwhile, PS titles this document window for that source file.

This situation lasts only up until the first save - which establishes an actual file name, which the PS document window reports thereafter..This will be a TIFF or PSD (typically). Even if you did override to JPG format instead, for this save operation - you would IIRC be blocked from overwriting the source camera JPG even then.

Consider what's seen when editing from a Raw image. PS could never directly open a camera Raw, let alone save changes to it, yet that still shows up as the document title initially. I like to say we are working FROM that Raw, not working ON that Raw. It's exactly the same situation with non-Raw imported files too.

After its file name has been established, we will from then on be editing and saving changes to that TIFF materially - the same as if we had opened it directly from PS.

I notice the same results in my system.

I suggest (only my thoughts) the difference is this-

"Edit a copy with Lightroom Adjustments"- is like editing (sending) a raw image file to Ps- the image data with LrC edits (that only exists in the Catalog!) is opened into the Photoshop cache until you actually decide to [Save] the new Ps file. LrC assumes you will be creating a (default) .psd or .tif from Ps. A preview thumbnail in not created in LrC until you finally do the [Save].

OTOH "Edit a Copy" - Does firstly create a new preview of the JPG file because it can create the preview from the JPG file existing on the Hard-drive. Then a [Save] in Ps will update the existing preview.

Sounds like it's using 'Edit Original'. If you are sure you did not select that by mistake, then perhaps you should try to reset the Lightroom preferences. https://www.lightroomqueen.com/how-do-i-reset-lightrooms-preferences/