1. Affinity Photo comes with Fill with Primary/Secondary colors shortcuts empty (only Shift+F5 for a somewhat complete but convoluted for simple fills tool). For people jumping from certain other softwares is a bit of a pace killer.
2. The problem is made worse because familiar shortcuts don't work: option+delete or ctrl+delete or cmd+delete will just delete the layer selected.
3. alt+enter, ctrl+enter or command+enter might have either another shortcut already or if it doesn't it does nothing.
Ended up settling for a temporary shortcut with option or control + backslash (alt+\), can get used to it but it maybe warrants a fix as it's a mayor friction point as soon as the program is just opened.