I’m no expert, but my personal endeavours of removing a drive chain of
bike has left it useless for re-use (using a chain breaker tool thingy)

I know that some new chains (non-Shimano) can had a real tigh
connecting link, which requires a lot of work to free-up after th
reinstall.
(Shimano chains have a funky link pin that’s tapers slightly so whe
installed it does seem to force the link plates together & bind).
There is the other type of circlip like connecting link which is
no-tools, no-brainer operation, SRAM?

Looking at the photos I would dismantle the rear derailleur for
clean-up & grease, & then spray the chain with WD-40 & turn it throug
a rag a few times

--
Marx SS