As @anon47616136 said, it’s more a privacy issue. I don’t have any security concerns with Google. To be fair, they no longer scan emails in order to serve you ads, so that was a big improvement a few years ago. They do, however, use all the other data collected on you to serve to serve ads, not only around the web, but in your inbox. For me, the nudge to move away from Gmail was when I’d had enough of seeing ads at the top of my email list that looked like just another message.
Google does provide tools to control various privacy settings and, if you set them correctly, they are still a decent option. I still use Google Photos, simply because I have every photo and video I’ve ever taken stored there and the search facility is unbeatable. I’m a bit annoyed at the removal of the unlimited free storage, though you still get 15GB for free and upgrading is very cheap - prices start at £1.59/month, or £15.99/year for 100GB.
The big tech companies know far too much about us these days. For me, Facebook is at the top of the pile and I use Facebook Container in Firefox to ensure I’m not tracked around the web. (Note, you don’t need a Facebook account for them to track you!)