Have you tried rebooting your phone? I sometimes lose third party app options in my share sheet. Once I reboot my phone, they are back (for a time...). I don't remember when this started for me, but it was after iOS 14 was released.
Wow, rebooting my phone worked — thank you @djs71a!
Yeah iOS 14 last fall seems to be when I recall first losing my Twitter share.
Shame that Apple (or Twitter, perhaps) appears to be getting sloppier with their code. Reboot needs apparently aren’t common just for Windows anymore. ??♂️