Nearly everyone always says to also combine a diet with exercise, but there's been a shift recently toward noticing that exercise energy budgets largely come out of the rest of your day for people who aren't primarily athletes[0]. Additionally, for many people, doing a little exercise on top of the normal day makes one ravenous, although I get that some people report a decrease in appetite as you did.

Google[1] finds a link that says that it takes 80 minutes to walk 8K steps at an average pace. Overweight people probably walk slower as a rule, but let's assume it takes an hour of just walking a day, if we take away whatever walking people are doing from the bedroom to the office to the kitchen to the couch. Even leaving aside the gym trip (and who among us doesn't have multiple uncancellable gym memberships? Oh, just me? :/ ), that's quite a time investment.

[0] https://www.science.org/content/article/scientist-busts-myth... [1] https://www.google.com/search?q=how+long+does+it+take+to+wal...