I want to choose Lemmy but I use Reddit more because Lemmy has technical problems, it keeps logging me out after days or few weeks, Reddit keeps my session for months or years
Staying here and reporting issues would help Lemmy, you know? Much more than just complaining it isn't as stable and mature as a commercial product developed by a company for years.
Logging you out from the website of your Lemmy instance or from a mobile app?
If the latter, try changing app. If the former, try contacting your instance admin, or see if there's a mod/admin community. Worst case scenario, move to another instance.