What a coincidence, I just opened a support request to MS because main M365 web apps (outlook, onenote) require re-login every 6 hours of "idle" (read: closed tabs). So on average, I login 3-4 times a day just into those two services (even though they use the same account, you need to login for each app individually!). Now for free/non-business users it seems longer sessions are possible, but MS claims there are 6hour limits for M365 subscribers [0]. As I am the M365 admin, it seems this setting is also not adjustable, but I will wait for the support response.
My experience in transitioning from GWorkspace have been horrible - M365 seems to be a patchwork from various MS products, bundled together but not nearly as consistent as GSuite. In the setup of my single-user, two-domain Email Account I had to login into 3 separate Admindashboards (Main admin portal, Exchange Admin Dashboard, new Security Center dashboard) for basic tasks. I encountered various errors and redirection loops, plus super outdated documentation/tutorials (link leading to nowhere, or documentation referring to older dashboard/uis). It seems M365 is just a mess at this point.
[0]: https://docs.microsoft.com/en-us/microsoft-365/Enterprise/se...