As someone who used Lotus Notes 6 for over 2 years at my previous job as the primary email client a few years back (think 2020s), no, it was not a pleasant experience to use Lotus Notes, especially since we had a O365 subscription for everything else and our major customer at the time was Microsoft. After a year at that job, it costed me so much productivity that I had to essentially jerry-rig desktop Outlook to work with the Domino server on my machine just so I don't have to fight it every step of the way.

The issue with Lotus Notes is that there was too much low-level machinery exposed directly to the client, and things you would expect to work with a basic email client, like .ics invites, simply never works right. There was no good dev environment for it, and most of the "develop your own app" feature was locked by corporate policy anyways so we pretty much had the worst of both worlds.

All in all, not something I would recommend to actually use, the only thing it really helped me see is that OneNote's lineage from Lotus Note as I think a lot of the original Lotus Note devs jumped to Microsoft at the time.