Learn Hardcore Chinese: wǒ xiǎng qù gōngyuán, bùguò wǒ jīntiān yào shàngbān. - I want to go to the park, but I have to work today.

想 = would like to / feel like; a softer desire or intention. Example: 我想去公园.
要 = going to / need to / must; stronger, tied to plan or obligation. Example: 我今天要上班. So the sentence contrasts a wish (想) with an obligation (要).

In 要上班, does 要 mean “have to,” “going to,” or “will”?

All are possible, but context picks the best reading. With 今天, 我今天要上班 most naturally means “I have to work today” or “I’m scheduled to work today.” It can also mean “I’m going to work today,” but the sense of obligation/schedule is strongest.

Is 不过 the same as 但是 or 可是?

All mean “but,” but the feel differs:

但是: a bit more formal/strong.
可是: more conversational/emotional.
不过: milder “however,” often softening the contrast. In this sentence, any of the three works: 不过/但是/可是我今天要上班.

Do I have to repeat 我 in the second clause?

No. You can say 我想去公园，不过今天要上班. Repeating 我 is also fine and can sound a bit clearer or more emphatic.

Where should 今天 go?

Neutral: 我今天要上班 (Subject + Time + Verb).
Emphasis on the day: 今天我要上班.
Avoid 我要今天上班, unless you say 我要上今天的班 (“I want to work today’s shift”), which is a different structure.

Do I need 去 before 公园? Can I say 我想公园?

You need a verb of motion or location. 我想公园 is ungrammatical. Use:

我想去公园 (I want to go to the park),
or 我想到公园 (emphasizes arrival),
or change the verb: 我想在公园散步 (I want to take a walk in the park).

Why 上班 and not 工作 or 去上班?

上班 = be on duty/at work; very natural for scheduled work: 今天要上班.
去上班 emphasizes the act of going to the workplace.
工作 (verb) is more general “to work”: 今天要工作 is also fine, just less shift-like.
去工作 is possible but less idiomatic for “go to work” in everyday talk.

How do I pronounce 不过? Is 不 pronounced bù or bú?

In connected speech it’s búguò (bú + fourth tone). Rule: 不 (bù) changes to bú before a fourth tone (e.g., 不去 búqù, 不对 búduì, 不是 búshì). Many learning materials write the base form bù, but you should say bú here.

Do I need a measure word for 公园?

Not when you’re just saying “go to the park” in general: 去公园. Use a measure word when specifying/quantifying:

去一个公园 (go to a park),
去那个公园 (go to that park).

Can I add 了? For example, 我今天要上班了?

我今天要上班了 adds a “change of state / it’s time soon” feel: “I’m about to go to work now.”
我想去公园了 means “I’ve now started to want to go to the park,” which is a different nuance from a general desire.

Can I use 虽然 … 不过 … to make an “although … but …” sentence?

Yes: 虽然我想去公园，不过我今天要上班。 You can also use 但是/可是 after 虽然. Keeping both parts is normal in Chinese.

Can I swap the clause order?

Yes: 我今天要上班，不过我想去公园。 Both orders are grammatical; the first clause gets more emphasis.

Is 我想要去公园 okay?

Generally avoid 想要 + verb in standard usage. Prefer 我想去公园 or 我要去公园. Use 想要 mainly with nouns: 我想要一杯咖啡. In some varieties/registers you might hear 想要 + verb, but it can sound redundant or less natural.