You can use software encoding. You would select "None" from the hardware acceleration drop down. Whether your old CPU is up to the task is another story.
Jellyfin 10.9.11
Ubuntu 24.04 LTS (bare metal)
Intel i3 12100 on Asus Prime H610M-E D4 mATX
32GB DDR4-3600
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
WD Green 3TB (Samba shares)
WD Red 3TB CMR (WIP Media, Test libraries)
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)
Fractal Meshify 2
Corsair CX430