I really appreciate your helpfulness, but made my choice a while ago. I am stuck with my phone plan for 2 years and am really dependent on good 5G.
Some time ago I also made a post on this forum to troubleshoot the problem (https://forum.sailfishos.org/t/cellular-connection-dropping-very-frequently), but at the time more people reported having an unreliable cellular connection. Combined with some other minor frustrations regarding Sailfish OS, i have just resigned for now.