I've used 'SPARK' ( as opposed to 'Spike') for a few years on iOS, iPad OS, and MacOS. It's clean, straightforward and has never given me the grief which others seems to have with 'Mail' or any other App... I use it for my GMail, and use 'Mail' for iCloud mail. The fact that Apple & Google aren't exactly bedfellows is IMHO the main issue with Gmail on Mail so I simply use what works & works very well. I am testing a Beta Dark Mode for Readdle ( the Spark people) which when fully introduced will have many new tweaks as well and probably change with phone settings re Dark mode. My daily driver mail program is 'Spark Dark' and it's very nice.