I can confirm this on slightly different setup:
With xubuntu-21.04, nvidia driver 470.57.02 (as well as 470.42.01 and 465.31 before) I see nvidia kernel module crashing with NULL pointer dereference.
I’m using 4K@120Hz on LG OLED48C1, there is also DP connected to older LCD panel which I don’t use.
GPU is 3080Ti (GeForce RTX™ 3080 Ti GAMING OC 12G Key Features | Graphics Card - GIGABYTE Global)
[Wed Jul 21 14:36:37 2021] NVRM: GPU at PCI:0000:01:00: GPU-1b78bb48-ea35-a89d-4855-3c25ece549c9
[Wed Jul 21 14:36:37 2021] NVRM: Xid (PCI:0000:01:00): 32, pid=5113, Channel ID 00000010 intr 00800000
[Wed Jul 21 20:08:18 2021] nvidia-modeset: WARNING: GPU:0: HDMI FRL link training failed.
[Wed Jul 21 20:08:30 2021] BUG: kernel NULL pointer dereference, address: 0000000000000000
[Wed Jul 21 20:08:30 2021] #PF: supervisor read access in kernel mode
[Wed Jul 21 20:08:30 2021] #PF: error_code(0x0000) - not-present page
[Wed Jul 21 20:08:30 2021] PGD 0 P4D 0
[Wed Jul 21 20:08:30 2021] Oops: 0000 [#1] SMP NOPTI
[Wed Jul 21 20:08:30 2021] CPU: 63 PID: 3708 Comm: Xorg Tainted: P OE 5.11.0-25-generic #27-Ubuntu
[Wed Jul 21 20:08:30 2021] Hardware name: ASUS System Product Name/ROG ZENITH II EXTREME, BIOS 1402 01/15/2021
[Wed Jul 21 20:08:30 2021] RIP: 0010:_nv002189kms+0x12/0x30 [nvidia_modeset]
[Wed Jul 21 20:08:30 2021] Code: c0 48 85 d2 74 07 80 7a 08 00 0f 95 c0 f3 c3 66 0f 1f 84 00 00 00 00 00 48 8b 87 20 7f 00 00 40 84 f6 40 0f 95 c6 40 0f b6 f6 <48> 8b 38 48 8
b 07 48 8b 80 10 01 00 00 e9 3c 76 76 f6 66 2e 0f 1f
[Wed Jul 21 20:08:30 2021] RSP: 0018:ffffb67150fe7ce0 EFLAGS: 00010246
[Wed Jul 21 20:08:30 2021] RAX: 0000000000000000 RBX: ffffb6715053e008 RCX: 0000000000000001
[Wed Jul 21 20:08:30 2021] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffb6715053e008
[Wed Jul 21 20:08:30 2021] RBP: ffffb67140d9e058 R08: 0000000000000000 R09: 0000000000000be8
[Wed Jul 21 20:08:30 2021] R10: ffff95ab4b854008 R11: 0000000000010004 R12: ffff95ab86757008
[Wed Jul 21 20:08:30 2021] R13: 0000000000000000 R14: ffffb67140d9d008 R15: ffffb67140d9d430
[Wed Jul 21 20:08:30 2021] FS: 00007fe72be14a40(0000) GS:ffff95c9fdfc0000(0000) knlGS:0000000000000000
[Wed Jul 21 20:08:30 2021] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[Wed Jul 21 20:08:30 2021] CR2: 0000000000000000 CR3: 00000001835a8000 CR4: 0000000000350ee0
[Wed Jul 21 20:08:30 2021] Call Trace:
[Wed Jul 21 20:08:30 2021] ? _nv002198kms+0x1ed/0x220 [nvidia_modeset]
[Wed Jul 21 20:08:30 2021] ? _nv002567kms+0x119b/0x1a80 [nvidia_modeset]
[Wed Jul 21 20:08:30 2021] ? __check_object_size.part.0+0x4a/0x150
[Wed Jul 21 20:08:30 2021] ? _nv000562kms+0x50/0x50 [nvidia_modeset]
[Wed Jul 21 20:08:30 2021] ? nvKmsIoctl+0x96/0x1d0 [nvidia_modeset]
[Wed Jul 21 20:08:30 2021] ? nvkms_ioctl+0x107/0x180 [nvidia_modeset]
[Wed Jul 21 20:08:30 2021] ? nvidia_frontend_unlocked_ioctl+0x3b/0x50 [nvidia]
[Wed Jul 21 20:08:30 2021] ? __x64_sys_ioctl+0x91/0xc0
[Wed Jul 21 20:08:30 2021] ? do_syscall_64+0x38/0x90
[Wed Jul 21 20:08:30 2021] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9