Our current target is 10.13 / High Sierra. According , the market share is about 5% (Catalina=81.7%, Mojave=6.23%), even with low specs . As a rule of thumb I would suggest to always support only one version backward.
This might have implications code-wise. Starting with 10.14, Apple introduced controlAccentColor  replacing selectedTextBackgroundColor that we use.
What is the rush to not wait until 7.4 is branched off in July 2022? The upgrade plan that would be introduced in 7.3 is here https://wiki.documentfoundation.org/ReleaseNotes/7.3#Platform_Compatibility
No negative comments were made on Ask LibreOffice or Reddit, but I hesitate to change the plan suddenly after already asking for feedback.
(In reply to Buovjaga from comment #1)
> The upgrade plan that would be introduced in 7.3 is here
This plan was the intention of the ticket :-)