I think 512mb is the tipping point. You really need a gig.
I run it on old 512mb HP 510 test laptop here but can't run Avast, which is the lightest weight anti-virus, without it bogging. I use Defender (built in, default) for protection and we have a hardware firewall.
I have taken it out on trips and it is perfectly sufficient for web surfing, spreadsheets, video watching, etc. It will even run two gadgets without maxing ram.
But I carry a backup image stored in a primary partition and my repair stick in case I get a virus, which I haven't so far.
I would buy more RAM but it is expensive for this lappy and I expect it to die any day.