That sounds particularly annoying!
I'm not aware I've ever used TPM 2.0 for anything, so I probably don't care. It's a requirement for official Windows 11 support, but my 7th gen. Intel CPU just misses out on support as well.
However, the story is a bit stranger than I'd remembered it. Under the aforementioned "if it ain't broke, don't fix it" doctrine, I hadn't bothered to upgrade the Dell BIOS since early in ownership. I run Linux full-time, and rarely boot into Windows 10. Windows updates only occasionally get installed, and I never bothered to pay much attention to the Dell updates mechanism that is pre-installed. Anyway, the BIOS revision that removed TPM was forced
installed since 2020, and I wasn't even aware!
Over in the Dell forums, there is some chatter of users downgrading to an old specific
BIOS revision to restore TPM. But if the offending update is a forced install anyway, this just temporarily fixes the problem, if at all. Another user also mentioned that the years of BIOS updates did have some useful bug fixes, which you lose by downgrading.
This was one of those quiet changes that Dell never described, or subsequently acknowledged. My best guess is there must be some security flaw in the TPM implementation that can't be fixed by firmware, so they decided to just disable it completely. Oddly enough, newer BIOS revisions than the one that removed TPM have not yet been quietly installed (nor do they restore TPM).