Thanks. This is what happened ~
rico@Sulaco:~$ 0ad
TIMER| InitVfs: 18.2078 ms
Writing the mainlog at /home/rico/snap/0ad/220/.config/0ad/logs/mainlog.html
TIMER| CONFIG_Init: 3.20412 ms
Sound: AlcInit success, using OpenAL Soft
TIMER| shutdown ConfigDB: 0.299 us
TIMER| resource modules: 3.00928 ms
TIMER TOTALS (9 clients)
-----------------------------------------------------
tc_pool_alloc: 0 c (0x)
tc_png_decode: 0 c (0x)
tc_dds_transform: 0 c (0x)
tc_transform: 0 c (0x)
tc_plain_transform: 0 c (0x)
tc_ShaderGLSLLink: 0 c (0x)
tc_ShaderGLSLCompile: 0 c (0x)
tc_ShaderValidation: 0 c (0x)
xml_validation: 0 c (0x)
-----------------------------------------------------
TIMER| shutdown misc: 226.053 us
TIMER| InitVfs: 174.242 ms
Writing the mainlog at /home/rico/snap/0ad/220/.config/0ad/logs/mainlog.html
TIMER| CONFIG_Init: 1.77505 ms
Sound: AlcInit success, using OpenAL Soft
si_init_perfcounters: max_sh_per_se = 2 not supported (inaccurate performance counters)
X Error: BadAlloc
Request Major code 149 ()
Request Minor code 2
Error Serial #105
Current Serial #106
UserReport.cpp(516): Assertion failed: "!m_Worker"
Assertion failed: "!m_Worker"
Location: UserReport.cpp:516 (~CUserReporter)
Call stack:
(0x55d4f01a7aee) /snap/0ad/220/binaries/system/pyrogenesis(+0x5a7aee) [0x55d4f01a7aee]
(0x55d4f014d401) /snap/0ad/220/binaries/system/pyrogenesis(+0x54d401) [0x55d4f014d401]
(0x55d4f014f48e) /snap/0ad/220/binaries/system/pyrogenesis(+0x54f48e) [0x55d4f014f48e]
(0x55d4efed36d3) /snap/0ad/220/binaries/system/pyrogenesis(+0x2d36d3) [0x55d4efed36d3]
(0x7fb27815d161) /lib/x86_64-linux-gnu/libc.so.6(+0x43161) [0x7fb27815d161]
(0x7fb27815d25a) /lib/x86_64-linux-gnu/libc.so.6(+0x4325a) [0x7fb27815d25a]
(0x7fb27a2ff888) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libX11.so.6(+0x40888) [0x7fb27a2ff888]
(0x7fb27a2ff9ba) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libX11.so.6(_XError+0x11a) [0x7fb27a2ff9ba]
(0x7fb27a2fc8eb) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libX11.so.6(+0x3d8eb) [0x7fb27a2fc8eb]
(0x7fb27a2fc995) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libX11.so.6(+0x3d995) [0x7fb27a2fc995]
(0x7fb27a2fd2c5) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libX11.so.6(_XEventsQueued+0x55) [0x7fb27a2fd2c5]
(0x7fb27a300085) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libX11.so.6(_XGetRequest+0x55) [0x7fb27a300085]
(0x7fb23b5bbbb2) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libGLX_mesa.so.0(+0x34bb2) [0x7fb23b5bbbb2]
(0x7fb27cdc97b3) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libSDL2-2.0.so.0(+0xcb7b3) [0x7fb27cdc97b3]
(0x7fb27cd9c746) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libSDL2-2.0.so.0(+0x9e746) [0x7fb27cd9c746]
(0x7fb27cd9e8e4) /snap/0ad/220/usr/lib/x86_64-linux-gnu/libSDL2-2.0.so.0(+0xa08e4) [0x7fb27cd9e8e4]
errno = 0 (?)
OS error = ?
AL lib: (EE) alc_cleanup: 1 device not closed
(C)ontinue, (S)uppress, (B)reak, Launch (D)ebugger, or (E)xit?
c
AL lib: (EE) alc_cleanup: 1 device not closed
rico@Sulaco:~
EDIT / UPDATE : I'm not allowed to post any more, as a new user I suppose, so instead i'll edit this.
I solved the issue & now the game plays fine - what I did was uninstall the Snap & instead select "ubuntu-hirsute-universe" as the source in Ubuntu Software.