compatible boards
if you don’t need nvidia, just get a cheap t470 board. you can see which of the below have a tpm at thinkpads.org with some finegling images for some parts seem presently at https://download.lenovo.com/Images/Parts/[model]/[model]_[idx].jpg where [idx] is A, B, C, … . many don’t have official part photos.
it looks like boards without nvidia have three large prominent empty chip footprints that are filled on boards with nvidia. the below are mostly listed as having nvidia. the numbers in the gaps have intel graphics and are also purportedly compatible. 01HX602 according to one site 01HX640 01HX641 01HX642 01HX643 01LV679 01AX967 01HX644 01HX645 01HX646 01HX647 01HX656 01HX657 01HX658 01HX659 01HX660 01HX661 01HX662 01HX663 01HX672 01HX673 01HX674 01HX675 01HX676 01Hx677 01HX678 01HX679 01LV675 01LV676 01LV677 01LV678 01LV679 01LV680 01LV681 01LV682 01LV687 01HX692 officially listed for tp25 01LV688 01HX693 officially listed for tp25 01LV689 01HX694 officially listed for tp25 01LV690 01HX695 officially listed for tp25 T480 boards start with 01YR and 01YU compatible laptops (note people have made the t480 interchangeable too)
T470 20HDCT01WW T470 20HES44K00 T470 20HDCTO1WW T470 20HES99L00 T25 20K70005SG