Hi Roff60,
Thank you for reaching Microsoft Community.
May I know which Bluetooth mouse and keyboard is this? Does it use a USB dongle?
Please run these steps on your Surface Laptop 3 and check if the issue persist:
1: Run Surface Diagnostic Toolkit and check Windows Update
2: Update drivers and firmware
Check what is the current OS Build of your Windows version by going to Settings > System > About.
Go to Download driver and firmware for Surface, choose Surface Laptop 3 then click Download on the next page.
Choose the .msi file that matches your current OS Build and click Next.
After downloading, run and install the .msi then Restart.
3: RunSystem File Checker Tool in Windows 10
Hope this helps.