These are two different things entirely which should not be compared.
If you like being on social media, there is nothing bad about be there if you have time for it, but the difference is that doomscrolling or what you call it is not involving money, but make sure social media does not affect your work and your sleep.
Gambling is also good if you do it in the right way. Social media supposed not to affect someone's gambling activities. Some people will like social media and also like gambling.
Doomscrolling has nothing to do with our finances and it can be seen as a way of life just like when you take some time to watch videos on social media just to have a relaxation. Gambling has been known to be a financial decision and anyone could either lose or win. Once you decide to gamble, you have planned to either make profit or loses although many players don't have that dogma of gambling to lose.
We all want to make money from betting which has two faces until we get one out of the two as result. Doomscrolling is preferably better since it doesn't require financial decision.