I have the Samsung Galaxy S9+. I got it last May as my graduation present to myself as I have never had a new/not buggy in some way phone. However, within a few weeks the phone was more laggy than any other phone I've owned including some that had some questionable viruses on them. I kept it updated, ran maintenance, and shut it down to restart at least once a week. None of this has worked. It will lag, crash many apps, and freeze to a point where it takes a few minutes just to get it to respond so I can restart it. Seeing as I paid for the 256 GB of storage and 6GB of memory I feel that I didn't get what I paid for in respect to actual functionality. For the price tag this phone has too many problems over a year after its release. If there is a way that I can fix these issues I would love to know, my phone is quickly losing any functionality and making texting, a most basic function, a challenge.
That's not a good Experience with your phone @FionaM
Let's see if we can help you with this !
Put the phone in Safe Mode which disables your downloaded apps and leaves the stock ones working which will help to determine if it's an app causing this.
If this stops in Safe Mode then come out of it and start deleting your most recent apps one at a time.
If it continues in Safe Mode then turn the phone Off and from a set series of button presses go into the phones file system and clear the phones system cache. This wont delete your personal info.
If that does not help then if you have a Sd Card remove it and see if the phone responds better which will help to rule out the sd card especially if you have apps moved to it. Also disable or remove any 3rd party launchers or themes you maybe using.
If still no improvement then with the sd card out back up and factory reset as a last resort.
Finally a Samsung Service Centre can run a diagnostic test on the phone.
My advice comes from being a UK Samsung Phone Owner.
I have no affiliation with Samsung.
Current Phone ~
Samsung Note 10 Plus 5G _256Gb >_ Samsung One Ui 2.5/ Android 10.