The M series processors are more efficient than Intel chips when it comes to memory management, not to mention significantly faster since you're dealing with unified memory.
I debated whether to stretch my budget and go for additional RAM when I got a new iMac a month or so ago. In the end, I ended up sticking with the stock 8GB of unified memory and upping the storage size and number of ports from the base model.
I have no regrets. There are times when I have quite a bit running at the same time including multiple MS 365 apps, a large number of browser tabs open in both Safari and MS Edge, MS Remote Desktop connected to multiple remote servers, etc. I haven't seen it bog down yet and memory pressure rarely ventures into the 'yellow' bar in activity monitor.
I've hear Apple say at 8GB on on M series processor will compare well with 16GB with an Intel chip. I believe it after working with both.