I don't understand it, because Tidyverse now appears to be incompatible with the version I have on my Mac (2023.09.01), but it worked fine last year, so why now?
If my Mac (OS v 11.7.11) was newer I would, of course, update to the latest version of R Studio (2026.04) like it keeps asking me to but my old Mac won't support it. Are there any versions between 2023 and 2026 that my Mac would support?
It's probably your R version, according to the screenshot you are trying to use R 4.5.3.
For macOS 11 the latest supported compatible RStudio version is 2023.09, which in turn supports R up to 4.3.1 (incl.):
If you do need RStudio as your IDE, try downgrading R to 4.3, current Tidyverse should be happy with anything >=4.1. Or if you do need a more recent R version, perhaps consider switching to Positron.