Everyone's privacy/security goals are unique, even the word "security" means different things depending on who's saying it. Using Brave browser as a pseudo-email client has helped me achieve some of my security/privacy objectives and I'll describe how I do it here. Maybe someone can apply part of it to their own approach.
I learned the hard way that associating all my online activity with one e-mail and using third-party logins, while convenient, is not in my interests. Now I like using several e-mails for different purposes. I think, if nothing else, people should consider having ONE email address strictly for banking (if you have to do online banking at all). You may want to use this ONE email for other sites you regularly do financial transactions with, but do not use it for anything else. Do not give it as a backup email, do not use it to send messages to friends and family. Banking and financial transactions only. I use an email w/ tuta.io for this and I like it, the downside is that tuta emails are not POP3, you either use a browser or get their app and you can't forward it. But VERY secure.
The other two I want to mention is proton.me (very secure and offers a selection of services in addition to email, I believe you can forward to/from. Proton is a little pushy about wanting you to upgrade to a paid account.), and zohomail.com (surprisingly secure, I guess they devote their energy to landing business accounts rather than collecting users data and spamming you). A bonus of getting an email with any of those three is you can probably get the address you want without resorting to 765dave_733@bigsite.com. Like there is a good chance the first name you want will be available on any of them. (zoho is solid e-mail with something like 5G of cloud storage and many features similar to gmail, but I would even say creating an account with them just for a burner if you need to give some website an email to create an account but don't require further communication from them)
So, okay, you have a few secure emails with some control over how your info is shared/accumulated and maybe you like using the apps they offer to access them. But another way that has worked for me is to use Brave browser (it could be some other one, but Brave works nice for this) and basically I log into all the sites and have my inbox on each, then set it to launch to those pages, then go through all the settings and lock it down as much as you can. I do not clear on exit though. I want it to keep the cookies it needs to log in whenever I launch it. For this I also use Brave's password manager (although you can use Bitwarden or some extension if you want).
PROS- you can really lock down this browser, also Brave will show a badge with a number indicating trackers/ads blocked which will help you determine straight-away if one of your e-mail's is garbage. Tuta and Proton are the only two I've experimented with which ALWAYS show a 0. CONS- It will take a bit of work to get setup and a bit of time to break the habit of clicking links, entering searches, and so forth in an open browser. If you want, you can do a bit of that, but in principle it's better to copy links and paste them into your main browser. Keep this one only for e-mail and maintain that seperation.
I experimented with many different e-mail providers coming up with this, and I also want to say stay the heck away from gmx.com and don't get the freebie add-on email w/ a vk.com account. Both horrible, not worth it even for burner email addresses.