Seems wpe wasn't built properly, having same issue building it from source, maybe a Gstreamer bug..?
WEBKIT_DISABLE_SANDBOX_THIS_IS_DANGEROUS=1 GST_DEBUG=3 LIBGL_ALWAYS_SOFTWARE=true XDG_RUNTIME_DIR=/tmp gst-launch-1.0 -v wpesrc location=https://www.w3schools.com/html/tryit.asp?filename=tryhtml5_audio_all name=s ! videoconvert ! fakesink s. ! audioconvert ! wavenc ! filesink location=mix.wav async=false
0:00:00.101268585 10 0x55cf795dfd30 WARN vadisplay gstvadisplay_drm.c:142:gst_va_display_drm_create_va_display:<vadisplaydrm0> Failed to open /dev/dri/renderD128: No such file or directory
0:00:00.104613145 10 0x55cf795dfd30 WARN cudaloader gstcudaloader.c:169:gst_cuda_load_library: Could not open library libcuda.so.1, libcuda.so.1: cannot open shared object file: No such file or directory
0:00:00.104639081 10 0x55cf795dfd30 WARN nvcodec plugin.c:94:plugin_init: Failed to load cuda library
0:00:00.121314879 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0x120000: 'AVR (Audio Visual Research)' is not mapped
0:00:00.121343467 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0x180000: 'CAF (Apple Core Audio File)' is not mapped
0:00:00.121348817 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0x100000: 'HTK (HMM Tool Kit)' is not mapped
0:00:00.121355896 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0xc0000: 'MAT4 (GNU Octave 2.0 / Matlab 4.2)' is not mapped
0:00:00.121360873 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0xd0000: 'MAT5 (GNU Octave 2.1 / Matlab 5.0)' is not mapped
0:00:00.121366209 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0x210000: 'MPC (Akai MPC 2k)' is not mapped
0:00:00.121371673 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0xe0000: 'PVF (Portable Voice Format)' is not mapped
0:00:00.121377324 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0x160000: 'SD2 (Sound Designer II)' is not mapped
0:00:00.121383895 10 0x55cf795dfd30 WARN default gstsfelement.c:97:gst_sf_create_audio_template_caps: format 0x190000: 'WVE (Psion Series 3)' is not mapped
0:00:00.416299326 10 0x55cf795dfd30 WARN default gstvaapi.c:231:plugin_init: Cannot create a VA display
0:00:00.425216356 10 0x55cf795dfd30 WARN msdk msdk.c:303:msdk_init_msdk_session: Failed to initialize a MFX session (undeveloped feature)
0:00:00.479164733 9 0x555b3b54e330 ERROR GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:570:gst_parse_element_make: no element "wpesrc"
0:00:00.480595757 9 0x555b3b54e330 ERROR GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1264:priv_gst_parse_yyparse: link has no source [sink=@0x555b3b808440]
0:00:00.482505031 9 0x555b3b54e330 ERROR GST_PIPELINE subprojects/gstreamer/gst/parse/grammar.y:1603:priv_gst_parse_launch: No src-element named "s" - omitting link
WARNING: erroneous pipeline: no element "wpesrc"
Seems wpe wasn't built properly, having same issue building it from source, maybe a Gstreamer bug..?