- some services don’t work (you already mentioned WhatsApp, there’s also others (Discord, FB Messenger) - maybe you can use them in the browser but it’s going to be a subpar experience)
- some have limited functionality (bank: works but you need to carry the physical 2FA device to log in instead of using your fingerprint; groceries: around here, the ones with websites have high order minimums and delivery fees; translating: camera translation (essential when travelling or living abroad) is only on the Google Translate app AFAIK; news: the national public broadcaster here doesn’t have a ‘breaking’ RSS feed, and apparently even the ‘all news’ feed is broken anyways)
- carrying around separate devices (camera etc.) brings us back to the original point: if you want to enjoy the niceties of modern devices, FOSS is going to be a compromise
Of the others, many depend on proprietary services, but pretty much all are accessible via their respective websites and I rarely see missing functionality.
payments - just use your card. You could even stick it in your phone case so you always have it if you have your phone
banking - there are some "app-only" banks where I live, but for every one there are 5 normal ones with websites
planning transit rides - all the ones I've used work in the browser
ordering cabs - around here they all have websites... or even phone numbers. Even Uber works via the website.
streaming videos and music - Spotify, YouTube, Twitch etc all work fine in a browser (in fact, on mobile they work better in a browser as you can block the ads!). If you want to host your own, there is Plex and similar.
gaming - most games won't work, but there are web-based and OSS games; Steam Deck could be an alternative
ordering groceries - around here they all have websites
ordering takeout - as above
translating documents - this one is weaker but there are several services that let you do this via the website
getting breaking news - if you really need to see them ASAP, use a site that has an RSS feed - they still exist! Might not work for local news though
taking (good) photos - plenty of OSS camera apps; using an actual camera could be an alternative
reporting vandalism to the city - must be specific to where you live; here everything is via web forms, and if there is an app it just wraps the website