Sorry, it is not the hardware acceleration. Strange enough, the slow startup only happens at first startup (some 30secs) and disappears thereafter. 

~$ snap run --trace-exec chromium
Gtk-Message: 16:49:03.254: Failed to load module "canberra-gtk-module"
Gtk-Message: 16:49:03.441: Failed to load module "canberra-gtk-module"
[3303:3303:0308/164903.689952:ERROR:edid_parser.cc(102)] Too short EDID data: manufacturer id
[3446:1:0308/164908.592828:ERROR:child_process_sandbox_support_impl_linux.cc(79)] FontService unique font name matching request did not receive a response.
[3446:1:0308/164908.606411:ERROR:child_process_sandbox_support_impl_linux.cc(79)] FontService unique font name matching request did not receive a response.
[3303:3433:0308/164910.260469:ERROR:udev_watcher.cc(96)] Failed to begin udev enumeration.
Slowest 10 exec calls during snap run:
  0.218s snap-update-ns
  0.387s /snap/core/8689/usr/lib/snapd/snap-confine
  0.178s /usr/lib/snapd/snap-exec
  0.679s /snap/chromium/1043/bin/desktop-launch
  0.214s /snap/chromium/1043/bin/chromium.launcher
  0.248s /usr/bin/dbus-send
  0.307s /usr/bin/xdg-settings
  37.788s /proc/self/exe
  42.106s /snap/chromium/1043/usr/lib/chromium-browser/chrome
  37.914s /proc/self/exe
Total time: 43.673s

~$ snap run --trace-exec chromium
Gtk-Message: 16:51:42.452: Failed to load module "canberra-gtk-module"
Gtk-Message: 16:51:42.460: Failed to load module "canberra-gtk-module"
[4082:4082:0308/165142.507754:ERROR:edid_parser.cc(102)] Too short EDID data: manufacturer id
[4227:1:0308/165144.923011:ERROR:child_process_sandbox_support_impl_linux.cc(79)] FontService unique font name matching request did not receive a response.
[4227:1:0308/165144.932876:ERROR:child_process_sandbox_support_impl_linux.cc(79)] FontService unique font name matching request did not receive a response.
Slowest 10 exec calls during snap run:
  0.168s /snap/core/8689/usr/lib/snapd/snap-confine
  0.025s /bin/ln
  0.428s /snap/chromium/1043/bin/desktop-launch
  0.037s /usr/bin/cut
  0.035s /usr/bin/dbus-send
  0.036s /usr/bin/dbus-send
  0.124s /snap/chromium/1043/bin/chromium.launcher
  3.882s /proc/self/exe
  5.419s /snap/chromium/1043/usr/lib/chromium-browser/chrome
  3.898s /proc/self/exe
Total time: 6.222s

~$ snap run --trace-exec chromium
Gtk-Message: 16:51:59.566: Failed to load module "canberra-gtk-module"
Gtk-Message: 16:51:59.585: Failed to load module "canberra-gtk-module"
[4299:4299:0308/165159.637753:ERROR:edid_parser.cc(102)] Too short EDID data: manufacturer id
[4448:1:0308/165201.970950:ERROR:child_process_sandbox_support_impl_linux.cc(79)] FontService unique font name matching request did not receive a response.
[4448:1:0308/165201.975635:ERROR:child_process_sandbox_support_impl_linux.cc(79)] FontService unique font name matching request did not receive a response.
Slowest 10 exec calls during snap run:
  0.166s /snap/core/8689/usr/lib/snapd/snap-confine
  0.025s /bin/ln
  0.426s /snap/chromium/1043/bin/desktop-launch
  0.037s /usr/bin/cut
  0.038s /usr/bin/dbus-send
  0.034s /usr/bin/dbus-send
  0.125s /snap/chromium/1043/bin/chromium.launcher
  3.159s /proc/self/exe
  4.570s /snap/chromium/1043/usr/lib/chromium-browser/chrome
  3.164s /proc/self/exe
Total time: 5.372s