Games drop framerate after a few moments

When I’m playing full screen games, after a few moments the game slows down harshly, and is practically unplayable.
The following games have had this issue, I don’t know if anything else is affected:
Cave Story (Linux Port)

Here’s my sys info:

      Kernel: 5.9.3-1-MANJARO x86_64 bits: 64 compiler: gcc v: 10.2.0 
      parameters: BOOT_IMAGE=/boot/vmlinuz-5.9-x86_64 
      root=UUID=2ed1c150-7de6-426c-942b-54053811cbdd rw quiet udev.log_priority=3 
      Desktop: Cinnamon 4.6.7 tk: GTK 3.24.23 dm: LightDM 1.30.0 
      Distro: Manjaro Linux 
      Type: Laptop System: TOSHIBA product: Satellite L55W-C v: PSLRAU-00J008 
      serial: <filter> 
      Mobo: FF40 model: 0692 v: 2.0 serial: <filter> UEFI: INSYDE v: 5.10 
      date: 09/21/2015
  Info: Dual Core model: Intel Core i3-5015U bits: 64 type: MT MCP 
  arch: Broadwell family: 6 model-id: 3D (61) stepping: 4 microcode: 2F 
  L2 cache: 3072 KiB 
  flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx 
  bogomips: 16766 
  Speed: 1955 MHz min/max: 500/2000 MHz Core speeds (MHz): 1: 1959 2: 1971 
  3: 1981 4: 1995 
  Vulnerabilities: Type: itlb_multihit status: KVM: VMX disabled 
  Type: l1tf 
  mitigation: PTE Inversion; VMX: conditional cache flushes, SMT vulnerable 
  Type: mds mitigation: Clear CPU buffers; SMT vulnerable 
  Type: meltdown mitigation: PTI 
  Type: spec_store_bypass 
  mitigation: Speculative Store Bypass disabled via prctl and seccomp 
  Type: spectre_v1 
  mitigation: usercopy/swapgs barriers and __user pointer sanitization 
  Type: spectre_v2 mitigation: Full generic retpoline, IBPB: conditional, 
  IBRS_FW, STIBP: conditional, RSB filling 
  Type: srbds mitigation: Microcode 
  Type: tsx_async_abort status: Not affected 
  Device-1: Intel HD Graphics 5500 vendor: Toshiba driver: i915 v: kernel 
  bus ID: 00:02.0 chip ID: 8086:1616 
  Device-2: Chicony TOSHIBA Web Camera - HD type: USB driver: uvcvideo 
  bus ID: 2-6:5 chip ID: 04f2:b446 
  Display: x11 server: X.Org 1.20.9 driver: intel unloaded: modesetting 
  alternate: fbdev,vesa display ID: :0 screens: 1 
  Screen-1: 0 s-res: 1366x768 s-dpi: 96 s-size: 361x203mm (14.2x8.0") 
  s-diag: 414mm (16.3") 
  Monitor-1: eDP1 res: 1366x768 hz: 60 dpi: 102 size: 340x190mm (13.4x7.5") 
  diag: 389mm (15.3") 
  OpenGL: renderer: Mesa Intel HD Graphics 5500 (BDW GT2) v: 4.6 Mesa 20.2.1 
  direct render: Yes