unless you are near the Cenotaph, or another war memorial around 11 am, there won't be any significant change from a normal Sunday.
If you are near church bells when they are pealing on Remembrance Sunday you may notice that they are "half-muffled", especially on cathedrals and larger churches which have enough ringers to prepare the clappers.
One thing I noticed about this weekend which is very unusual - I had to pop into a John Lewis yesterday for a couple of lightbulbs (first time for me into a department store since February 2020, but I had to) and the queues at the checkouts were absolutely huge. People are scared that supplies will be scarce near Christmas and moved last minute shopping up 6 weeks. The mall was absolutely heaving.
I hate panic buying - now the new normal. (Nigel steps off soapbox)...