Haven't tested yet, so only comments from reading the code and the screenshots.

Please bump the frameworks version to 5.45, otherwise the icons look totally different.

I just wondered about the border around the repeat and shuffle buttons. Since borders are removed everywhere else, I think it may be better not to add them there again. Also one comment inline

Regarding the icons, unless we start bundling our own icons, we're settled with these. You could try making the next and prev icons a little bit smaller like before.

The way random and continue buttons work is very nice. It is very easy to understand in which state they are. I think that even though they mostly indicate a state, they are easy for the user.

In D12714#258646, @astippich wrote:

I just wondered about the border around the repeat and shuffle buttons. Since borders are removed everywhere else, I think it may be better not to add them there again. Also one comment inline

The border groups the shuffle/repeat buttons and helps separate them from the burger/volume. Here's a screen without the border for comparison:

We could also try using a slightly darker background instead of a border (open to suggestions tho).

In D12714#258932, @mgallien wrote:

The way random and continue buttons work is very nice. It is very easy to understand in which state they are. I think that even though they mostly indicate a state, they are easy for the user.

I like this way too but Alexander's suggestion has an interesting benefit: if we have more repeat / shuffle styles in the future (repeat-album, repeat-once, etc.) we can cycle through icons. We wouldn't be tied to only those two states.

The repeat/shuffle issue is an example of the problem of not having a proper segmented control style widget. See https://bugs.kde.org/show_bug.cgi?id=384514

I remembered why I wanted to implement them as toggle button: For the play controls on the left, the reduced opacity of the icon indicate a disabled button, e.g. non-clickable button. Contrary, the repeat and shuffle buttons are always enabled. I think it would help explaining the behavior more clearly.

Another idea: the repeat and shuffle buttons can be moved to the left of the volume slider and mute icon. The menu button would then be separated clearly. If the shuffle/repeat buttons are then implemented as toggle buttons, we would also have three of such buttons nicely grouped together.

In D12714#258961, @januz wrote:

In D12714#258646, @astippich wrote:

I just wondered about the border around the repeat and shuffle buttons. Since borders are removed everywhere else, I think it may be better not to add them there again. Also one comment inline

The border groups the shuffle/repeat buttons and helps separate them from the burger/volume. Here's a screen without the border for comparison:

We could also try using a slightly darker background instead of a border (open to suggestions tho).

In D12714#258932, @mgallien wrote:

The way random and continue buttons work is very nice. It is very easy to understand in which state they are. I think that even though they mostly indicate a state, they are easy for the user.

I like this way too but Alexander's suggestion has an interesting benefit: if we have more repeat / shuffle styles in the future (repeat-album, repeat-once, etc.) we can cycle through icons. We wouldn't be tied to only those two states.

I must admit that I have a strong preference for the version with borders around the shuffle and continue buttons.

I tried with reversed layout (RTL support) and the margins are wrong.
You can test by starting elisa with the -reverse option :
elisa -reverse

In D12714#259483, @mgallien wrote:

I tried with reversed layout (RTL support) and the margins are wrong.
You can test by starting elisa with the -reverse option :
elisa -reverse

Ah thanks! I was missing that trick, I'll get it fixed then

In my opinion the read cross is fine, and we kind of have the same situation already with the mute icon.
Using desaturate may also cause issues with other icon themes.

Otherwise looking really good.