Hmm not sure I agree with the whole "you must be well jell" comments.
No there's nothing 'wrong' with putting up photos of yourself traveling online. As people have said, it used to be getting everyone round for a slide show of your holiday or getting people to look at the holiday photo albums.
It only becomes a problem for people who can't think critically about SM who see someone's highlight reel or influencers who simply fake their content (eg hiring private jet sets to pose in as if they're going somewhere amazing when they are very much on the ground) and assume frequent travel is normal. It isn't the norm for the majority of people. Mumsnet tends to have a more affluent demographic, so few people here living hand to mouth, so there may be more people here who can travel a lot.
The other issue is when people post publicly, revealing "hidden gems", which gets them a lot of likes and views but then leads to excessive bumbers of tourists going to specific, previously little known areas. Heavy footfall in natural areas along with people naturally needing to eat and go to the toilet, means some areas cannot cope. OF COURSE, NOT EVERY PERSON POSTING THEIR HOLIDAY SNAPS ONLINE CONTRIBUTES TO THIS PROBLEM (had to capitalise and bold that before anyone starts jumping up and down 😂). But it is a problem and not down to envy / jealousy that some people don't condone it.
It depends if that / how much any of that bothers you.
I barely use SM and don't follow any travel pages for this reason. I'm not jealous or envious. I've traveled a lot out of necessity (born in another continent, lived abroad in Europe, grew up in NI, uni in England and France, worked and lived in Scotland for years, in South America for a few months yada, yada, yada).